The somatotype system classifies the human body into how many categories?

Most people are unique combinations of the three body types: Ectomorph, Mesomorph, and Endomorph. Nutritionists, exercise physiologists, and even doctors use this classification system to help design effective, individualized fitness plans.

Explanation:

don't worry, but do consult a doctor.

explanation:

having a high metabolism at age 13 is not abnormal.   however, if you are concerned, do consult a doctor.   the doctor may identify a correctable issue, and then you'll have your answer.   in the meantime, there are a few steps you might consider.

first, reflect on just how much physical activity (work out and dancing) you are getting relative to your caloric intake.   keep in mind that if you are interested in gaining weight, you must have a higher caloric intake than output.   second, if eating robust healthy meals is not providing enough calories, you'll need to include high caloric, yet healthy, snacks.   i warn against using an over the counter high-calorie supplement (drink or food) until you have consulted a doctor.  

answer; mistrust of the health care system;