You have lots of good feedback from Sarahjogs already. I would just add that the only time TSh is useful as a diagnostic is when it is at extreme levels, confirming overt primary hypothyroidism. All other forms of hypothyroidism need to be diagnosed and treated based on symptoms, along with levels of the actual thyroid hormones, Free T4 and Free T3. Free T3 is the biologically active thyroid hormone that essentially creates the metabolism of your body. Free T3 is that important, yet most doctors don't bother testing and largely ignore it.
You don't necessarily need an Endo. they are typically rigidly depend on TSH for diagnosis and treatment, which does not work for most hypothyroid patients. To understand what is needed, I suggest reading my paper, linked in the first message on this site.
https://thyroiduk.org/further-reading/managing-the-total-thyroid-process/
I'm not going to comment about the thyroid hormone levels because there are people on here that know a lot more than me about that (although your TSH is high and would indicate hypothyroidism, especially if your free T4 is in the bottom half of what your lab considers "normal range").
I just wanted to share what happened with me since you mentioned irregular menstrual symptoms that might be related to hypothyroidism. I had very heavy, and prolonged periods (lasting 18-20 days, they were only very heavy for a small portion of that time), which got much, much worse after my thyroid was removed in 2018. It took about 6 months for me to get back up to a "normal" thyroid hormone level after my thyroidectomy completion surgery. My endocrinologist told me the heavy periods were a hypothyroidism symptom and should go away when I got to a better thyroid hormone level, but they did not go away (they also made it impossible for me to get to a stable thyroid hormone level because I was losing so much blood every month, and, despite me telling all my doctors about my heavy periods my PCP, ENT, and endocrinologist did not bother testing me for anemia, I would not find out I was anemic until after 2 thyroid surgeries and a full 20 months later).
I finally (after having an extreme anxiety spiral that I'm pretty sure was due to dysregulated estrogen levels) went to the gynecologist, terrified that my very heavy bleeding (which unbelievably got worse towards the end of 2019) was caused by something like uterine cancer since I was "no longer hypo" -- please do not think your irregular bleeding is caused by cancer - a lot of things can cause heavy/irregular bleeding, but in my anxiety spiral my brain jumps to the worst case scenario, and that just fuels the spiral.
It turns out that I a.) was anemic, and b.) had a very large fibroid. I don't know what caused the fibroid growth, but I do know hypothyroidism can cause very heavy and prolonged periods (which I had for years leading up to my eventual thyroid diagnosis), that the heavy periods are thought to be related to estrogen dominance (higher estrogen to progesterone ratios than what is normal), and that higher estrogen levels are also thought to fuel fibroid growth. After an exploratory surgery in Jan 2020 (where I learned I had a huge fibroid and was told I would probably need a hysterectomy) and months on estrogen suppressing drugs (so they could safely remove the fibroid and not do a hysterectomy), the fibroid was removed, my thyroid hormone levels stabilized, and my periods have returned to completely normal, and a lot of my hypothyroidism symptoms went away (I still get afternoon fatigue almost everyday, but it is a lot less than it used to be). I'm also experiencing much less anxiety in general -- I do not know if this is because a.) my estrogen levels are less erratic or b.) I'm finally healthy after several years of major health issues. It is incredible how much my hypothyroidism over the past several years probably fueled my anxiety - I have a very different perspective now in hindsight - physical health and mental health are tied together in so many ways, and I think in my case, my anxiety was hormone related, and now when people talk about a "mental health" problem as if it is a less legitimate health problem or a character flaw, I get frustrated. Mental health is health.
Anemia plus hypothyroidism can exacerbate many, many hypo symptoms, and I think this is what made my life a living hell for about 1.5 years after my thyroid surgery. (It also made it much harder to get to a stable thyroid hormone level.)
Why am I sharing all of this? If you suspect your prolonged bleeding is related to your thyroid hormone levels, I recommend getting it checked out sooner rather than later, just to make sure that hypothyroidism is the cause and rule out other potential causes like fibroids or polyps, or something else that can cause irregular bleeding. (I had three periods - one in December 2019, two in January 2020, where I thought I might pass out because there were 36-48 hours of extremely heavy bleeding each period. The volume of blood coming out of me was horrific, and unbelievable to think about now, in hindsight. It is amazing I did not need to go to the ER.) This was a fixable problem for me, but I wished I had gone to the gynecologist much, much earlier, I just thought (and was told by doctors) that my menstrual problems would resolve themselves when my thyroid levels stabilized. (I did have a gynecological exam by my PCP in March 2018, when I was experiencing these problems, and shared just how heavy and prolonged they were, but in hindsight really wish I had followed up by going to a gynecologist after my June and August 2018 thyroid surgeries - I was so hypo and so focused on fixing the hypothyroidism and just getting through each day at that time, and convinced if I fixed my hypothyroidism my periods would go back to normal. I was also not thinking clearly for a very long time).
I'm not saying that you have a fibroid, I just thought I'd share what happened with me and recommend you at least get the menstrual issue checked out, even if you can't get your hypothyroidism treated in the meantime. I don't want someone else to have to go through what I went through if it is preventable.
A period lasting 3 weeks is not normal.
I'm sorry you are going through this - when I first went to the doctor for lumps on my neck (which ended up being a multinodular goiter) and with my heavy/prolonged periods being one of many hypo symptoms, my TSH was 3.14 and I was told this is "normal" and that I didn't have hypothyroidism. It turns out my thyroid was extremely inflamed and being destroyed by my immune system (so much so, that to determine if one of my suspicious nodules was cancerous after removing half my thyroid, they had to send pathology out to a different hospital for a second opinion because too many immune cells were making it hard to determine what was going on in the nodule, and my ENT/thyroid surgeon, who does hundreds of thyroid surgeries a year, commented about how inflamed the whole thing was). Doctors, for whatever reason, often don't believe patients when they talk about their hypothyroidism symptoms, and it is extremely frustrating. I walked out of my endocrinologist's appointment in August 2019, a full year after my second thyroid surgery, in tears because my endocrinologist and the resident did not believe I was hypo based on my tests, despite telling them about the extreme afternoon fatigue I was still experiencing, and all the cognitive and menstrual symptoms. I'm 90% sure my gynecologist did not believe me when I told her about my very heavy and prolonged periods (did not believe they were "that heavy" or lasted that long) until the exploratory surgery in Jan 2020, where she discovered a huge fibroid (which they removed part of but had to stop during that first surgery because it was bleeding so much).
I don't know how much of my anxiety was fueled by doctors constantly telling me that I was fine, that I wasn't experiencing the symptoms I was experiencing, and family members not understanding what I was going through and constantly telling me I should "try harder" to not be extremely fatigued in the afternoon, but it certainly wasn't helping.