Food problems. Please help

So this has happened to me twice before. Today I ate breakfast(cereal) at 5:15ish. Then I went to school. During my second period, I got really hungry at around 8:45ish so I ate some grapes. But then in the next hour or so I felt really nauseous and felt really warm. I went into the bathroom to try to feel better but I couldn't. So I went back to class still feeling awful. I felt like that all the way up to lunch, which is around 11:40. I ate lunch (pb&j sandwich with peanut butter crackers and an apple) and I slowly felt better. This has happened to me before; but I finished up cross country practice instead of being at school. But I was drinking water both times, I'm not on my period, nor am I even being close to pregnant. So what's wrong with me??