Very thin naturally and always lose energy... Help!

I'm very thin naturally at about 5'7 and weigh 118 but it has been known to fluctuate between 120 and 107... so right now I'm at my favorite size, although I'm so jealous of you curvy women out there!

Anyway, I eat roughly 2000 calories a day, sometimes more since I often don't read labels, and eat out alot since I'm a full time college student and full time worker. Often I lose energy really bad during the late afternoon, early evening, and really want to know how to fix that. I'd like to know anyone's opinion of how to improve my energy with certain foods, water, sleep etc... any help is much appreciated!

Can you give us a sample menu for a day?