I have taken thyroid medication since I was 13, I'm almost 53. Still thin, not skinny anymore.
As a teenager, things are going to change dramatically as you mature. Get a good checkup, a complete blood workup, every year or so. Eat healthy, with plenty of fresh fruits & veg, brown rice, baked potato...avoid fad foods & drugs of any kind. You're still growing, don't do anything to throw things out of balance. Things will "level out" in time if you'll just be patient.
One other thing - please STOP paying attention to anyone who doesn't know you or your situation who say mean things. Lots of people get a real thrill out of meanness, but you'll be better off to ignore them.