Nauseous After Eating

Hey, question; does anyone else get nauseous after eating?
I tend to get nauseous and vomit on my period, so I don't eat well at all; almost nothing since I can't keep it down D:
But now that my period is finished, I get these 'nausea spells'. I'll feel gross in the morning and can barely down a cup of coffee. Then I'll feel fine and eat lunch, then feel gross and vomit-y again. It's been like this for a week, but I'm not sick or showing any other symptoms; no headaches or runny nose, so I guess it's not a virus. I wish I was just sick so I could know there's an end to this. ):<
My running workouts have been suffering because I'm not eating enough.

(No I'm not pregnant; this isn't morning sickness.)

Thanks in advance.