Lossing concentration

Patient: I am 17 year old boy studying for +1. i used to have classes whole week. i could not concentrate for a certain period of time, i feel sleepy, even though the class is understanding. my teachers shouts at me and often send me to wash my face. i feel bad. i have passed my 10th exam with full grade. now am focusing for entrance. but the sleep wont allow me to concentrate in class. i used to sleep atleat 6hrs.pls tell me what can i do?