As someone who has been running off and on since high school, a few reasons come to mind.
1. In your post you say "everytime I
start running again". This means that you have stopped for a period of time. It's possible that your body is not conditioned for you to run long distaces at the frequency and pace you have been running. I have found that, for me, running everyday after picking it back up leads to tiredness. However, if I ease into it by running every other day (or cross train) with less mileage, then I don't get quite as fatigued at the end of the day.
2. Try to run earlier in the day opposed to at night. Legs need to recover and "cool down" after bearing so much stress. If you run right before bed, your legs don't recover properly, and they might be unconsiously active during the night.
3. For me, my lifestyle in college was much different than in high school (a.k.a.: beer and other forms of alcohol). Booze has been known to weaken legs and make one more fatigued.
4. You could be on to something with campus food. I don't remember it being the most nutritious food available. Perhaps you could modify your diet to include healthier foods, especially those that promote energy and muscle recovery (fiber, fruits & veggies, nuts & seeds). This might be difficult considering a college student's budget and resources.
5. I'm assuming that you've grown a bit since high school? Perhaps your body isn't used to carting that extra weight around. Perhaps you just need to build up the running muscles that you haven't used in a while.
Start with these possibilities. If you can refute them all, then I'll come up with a new batch of reasons for you.
