Help! I'm exhausteddd

Ok so, I am in high school and everyday that I get back home from school I fall asleep. I can't help it I am just exhausted completely. I don't understand why?? This has been happening for about 1 year now and It's very difficult if not impossible for me to stay awake once I get home and coffee makes me nauseated. And once I do fall asleep I end up sleeping for several hours at a time. Anyone else with the same problem?