1. Where exactly is the pigmentation on your body? 2. Since when is the pigmentation on your body? These questions ARE VERY IMPORTANT and need to be answered for any dermatologist to help you. Plus, without examining the type of pigmentation it is difficult to diagnose why you have the pigmentation in the first place. You say you have recently started thyrox . So there are OTHER associated autoimmune conditions that can cause specific types of pigmentation. So visit a dermatologist near you. Only procedures will never help. Get yourself examined and you should benefit, but only after being diagnosed.
Start using a spf 40 sunscreen for your face and open parts like neck and arms 2 to 3 times daily.
As you have autoimmune thyroid Pls get evaluated for metabolic syndrome first.
Then start with non steroid based lightening agents.
Chemical peels. IPL treatments and Microdermabrsion are some treatments to reduce blemishes.
See a dermatologist near you.