If you’re going vegan, I’d strongly suggest you take a
vitamin B-12 supplement.
B-12 comes from animal products, such as red meat, eggs, dairy, etc. B-12 deficiency can have many of the same symptoms as hypothyroidism (fatigue, neuropathy, etc) so you need to make sure you get a good supplement. I recommend, either, chewable or liquid and make sure it’s Methylcobalamin, which is readily absorbed.
Let us know how it works out for you.