Wow, thanks so much for the info! I was really aggrivated by how the doctors just completely dismissed my suggestion that it might be the meds he was on. He was originally on Adderall and was really skinny, but the side effects were awful. At the time his weight gain started, he was on metadate. Now he's on focolin. I kept trying to tell them that his eating habits, exercise habits, etc - nothing had changed except for the change in meds, but they just basically told me I didn't know what I was talking about. And these were doctors at one of the world's leading hospitals for children, so I didn't argue.
But I will definitely get his thyroid checked. With all the other social issues he has, I don't want his weight to be one of them. Not to mention all the health risks.
Thanks for letting me know there's a chance I may have been right and not just being a "mom"!