Lately I've been having these days randomly where I'll be found for half the day and then the other half of the day I end up becoming really nauseous and I actually feel like I'm going to do IT. I never have, but they always seem to come right before my period or in this case right when I'm ending it and it's become really frustrating because it ends up that I can't sleep or eat for a day or so because I'm so scared. Does this happen to anyone else and what do you think causes it?