Eat too much sugar and then you gotta worry about diabetes
. Well, okay not really, but if it runs in
your family you might.
Really, though, I'd have your doctor check your thyroid levels. You might have a thyroid problem. Or you might have a really high metabolism. See a doctor. There might be many reasons. Type I diabetics lose weight I think instead of gaining, so maybe you are diabetic type I? That's the children's diabeties, but it can have a later onset, during the teen years.