Going on 4 months no period...

Okay ladies, I have a question...any advice is helpful. My last period was March 29th. I still have yet to get my period and we are now in July. I do not spot, I have menstrual cramps at times. I have had sex, unprotected with my fiance, whom I've been with for 5 years. He recently had surgery and we found out he's sterile. I've taken numerous pregnancy tests and I'm not pregnant. Since then he's cheated on me so I left. About a month ago. Still no period, but I have been extremely stressed and gained some weight due to stress eating and my depression. I don't know what is going on with my body. I've scheduled a doctor's appointment, but so far each time the doctor says I'm fine. No rhyme or reason. Any advice and/or theories? Please help..