Menopause is quite likely..some women enter earlier than others. Your doctor can run a panel and tell you if you are premenopausal. Also, if you have ever been treated with "lupron depot" during chemotherapy, there is a high likelihood of early menopause. This was my case and I lost my period at 42.
45 is really early for menopause. And usually it is something that takes place over years (plural) time. Agree that a doctor can tell you if you are indeed starting menopause. My pattern as I go through menopause is actually super heavy periods. Like triple homicide if you know what I mean but only for shorter times like 3 days max. I have cramping and bleeding like I never had before. My doctor says this is a common pattern. I'm regular though. My good friend had her periods just peter out and come less and less and were shorter and shorter until they were gone by 52 years of age. Your hormones are also shifting at all times as we age. The spotting is indicative of that. Too much progesterone can cause the brown spotting you describe.
So, see your doctor to have the levels checked and you'll know where you are at and what adjustments may need to be made in order to make this stop. Let us know what the doctor says!
OMG, so young. But it can happen. I'm older than you and still in the throws of it all starting and have been for a few years. Pain in my butt. LOL So, yep. I'd say your period is the victim of hormonal changes. Heavier bleeding when on a period is common or menopause AND spotting like you describe also can happen. Talk to your doctor next time you see them. Mine says my few days of heavy bleeding are normal even though I went through 40 plus years of a different type of period preceding it.
There is also an early study that shows that long term usee of oral contraceptives can advance the onset of menopause.