Okay so, i haven't really eaten anything in two days, but today whenever i actually eat a meal i feel really nauseous after. is this because i only ate around 200 calories the two days before? how can i prevent it from happening now

That's because your body is overwhelmed. You can avoid this from you know, eating everyday. Even it's a little HEALTHY snack, like an apple or something. Eating a snack isn't going to excuse all the nutrients that your body needs, if you have a healthy diet you'll be just fine. I wouldn't recommend going days without food though, especially water.