Always exhausted! help!?

i used to kind of put off my exhaustion as normal, but it's gotten to the point where it's not. I often sleep 9-11 hours each night an still feel tired during the day, I even take naps a couple days a week. My life is not stressless, i am in college, but it is nothing unmanageable. Often after two cles I will come back home and have to sleep an hour or two to feel energized again. I eat pretty well (am vegetarian (but no iron problems)) and exercise alot, around six times a week. I never feel tired while working out, but afterwords i often do. I do have allergies, and take claratin for them but I don';t know what it could be? my grades are really suffering, and I'm 21, i should be able to get by on 7-8 hrs a night during the week!!??? what is wrong?