What Causes Dark Underarms And Thighs?

I have a dark neck, darkness in underarms, and between thighs, including skin tags to go along with this. I haven t had my period in 2 years and i have only started it twice. I have hair growing on my chin, chest, and breast. I recently had a blood test they said i have a low thyroid. I have semi bad acne on my buttocks, back, and of course face and a little between my thighs. I have an increase amount of hair growth when i shave my legs and i would just really appreciate it if you could help? I was also wondering if any of the problems you think i could possibly have be the cause of my migraines too?