What's upsetting my stomach? Nurse/Doctors' answers welcome!?

My stomach has been upset and gy since yesterday...I haven't felt sick enough to throw up, but it's enough to make me feel under the weather. I'm still eating, but I have smaller appetite than usual. Is this likely to be a stomach virus, or could it just as well mean I'm not used to the food at my new college? It's definitely less healthy than what I eat at home and has a lot more fat and refined grains/sugars in it. I'm hoping I'm not sick with something, so I thought I'd throw the question out. Also, if I'm sick with a bug, can I still be around people as long as I keep my hands sanitized and don't breathe in their faces?