Hi, Emilie,
So sorry your thyroid problems have manifested in your hair. I have thyroid disease and suffered some serious hair loss last year. I would recommend treating your hair as gently as possible. Don't use a brush... just use your fingers or a wide-tooth comb to detangle your damp curls. Also, be sure to hydrate your hair often... hair oils and leave-in conditioners should help.
Hope this helps! Best wishes.