Late periods

Briana
I've talked to my doctor but I want the opinions of some fellow women. Please don't bash my post its childish. I turn 21 in December and my fiance and I have been trying for two years. I'm 8 weeks late on my period. I've taken several pregnancy tests and they are all negative. I've had a blood test and its negative. I've had an ultrasound and they can't find anything. I've had some serious bloating and cramps in my left side right above my hips. My heartburn is sooooo bad that it keeps me up at night even with antacids. I can't stay out of the bathroom and I'm always nauseous. The tiniest smallest little things that my SO does, bothers the shit out of me and even so to the point were it pisses me off. I can't sleep and I'm always hungry. What could cause something so close to pregnancy if I'm not pregnant?