Goolara pretty well said it all--- I am hypo/Hashi and have both low vitamin b12 and vitamin D. I've been on b12 shots for over 2 years (should have been a lot longer) and just recently found out about my vitamin D deficiency, so have not started a treatment for that yet. In fact, that reminds me that I need to call the doctor about that............................lol I'm finding that both vitamin b12 and vitamin D deficiency can cause fatigue just as hypothyroidism can.
I agree with goolara that you can't treat the Hashi per se, but you'll most likely get treated for being hypo and that once your levels are right for you, your symptoms should go away.
Did you get your actual thyroid levels checked? Free T3 and Free T4, along with TSH? If not, you'll want to get those levels tested as well so you can make sure you get treatment as needed.
When you get your labs, make sure you get a copy for your records and if you like, feel free to post them here and members can comment.
You cannot treat Hashi's, per se. Once you have antibodies, you have them for life, unless your thyroid is removed for some other reason or it it totally destroyed by the antibodies (at which time they go into remission). However, if you have Hashi's, you will eventually become hypothyrod (if you are not already). Hypothyroidism can be treated. So, the symptoms of Hashi's end up being treated, but not the underlying cause.
It's great that your doctor tested D and B12. Many people who are hypo are deficient in one or both of those, and it's good to know where you stand on them. Supplementing D and B12 will not improve your thyroid condition, but it helps bolster your overall health and can enhance the effects of thyroid meds. Also, some of the symptoms of hypo and deficiencies in these vitamins can be the same.