Its called being young. When I was at school Id get up at 7, go to school, home by 4, sleep till 8, out til 10 and in bed by 10.30 and I still fell asleep in class. Teenagers sleep more than any other age group. Even now I get drowsy mid afternoon and still nap when I get in. Some people need more sleep than others. If youre worried though go to your doctors for a check up.