Make a good list of things you do enjoy, things that make you feel better, a kind of notebook of ideas to try? "Exercise" is good but make a plan too, so you can try "go to the pool and swim laps" or something and know how to put it in place. If I were to say to myself right now, "Oh, I'm feeling a bit down, I'd better go exercise" I would probably end up doing nothing :-) Or, if I had to find more fruits and vegetables from my dorm, that might prove difficult if I did not have an emergency stash of cash for the grocery store or a restaurant (I taught myself to eat liver when I was in college; got all those good B vitamins :-) and a plan of what friends would go down to town with me, etc. I probably would not go do that either.

How about friends to study with? That always helped me when I was feeling more depressed than usual. Being around people helped me keep moving on in a more even keel than trying to generate the energy all myself to study.