Why am i so hungry after school?

ok well when i wake up for school, i have breakfast sometimes.. then at lunch at school, i usually have a pop-tart, a juice, and a snack. when i get home a get a snack. but sometimes i am still hingrey and then i eat more and more.. I am not fat, i am skinny. i am ten and 61 pounds.. so why am i sao hungrey?