weight gaining for 3yr old

My son turned 3 today he 44 pounds, he is very active never sits down unless sleeping. He doesn't eat that much and doesn't eat cookies or any thing to do with pastries. He keeps gaining weight and complains of his stomach hurting. I was thinking maybe there is something wrong with his thyroid but his doctor says he is overweight, but healthy. Thyroid problems run in the family, his grandmother has thyroid problems now. Could there be something wrong or am i just worrying for nothing.

[Kevin Kennedy, Ph.D.]

Dear Robin,

Has lab work been done to rule out any thyroid problem, and your deoctor's reassurance is based on such results? Or is he offering you his clinical impression? If no diagnostic lab work has been ordered, it might make sense so that you know you are covering the bases, particularly with the family history. While your son's weight is, as you know, above the maximum one might expect at his age, it's not so far above that it warrants alarm. But you are asking sensible questions, and if lab workups support the doctor's impression, I'd relax about it.