Endometriosis?

So I stopped birth control about a year and a half ago. Until about 4 months ago my periods were not regular and I would get painful cramps. Since my periods have become regular the cramps have been getting worse. So bad that last month I was at school and I passed out in the bathroom because of the amount of pain I was in. I went to the hospital and they gave medicine and did an ultrasound and an exam but I got no answer for why I was in so much pain. I have gone to my OBGYN a lot but she does an exam and says she can’t feel anything wrong. I have been three times in one month to be exact. I also have pretty bad cramps from the time I ovulate until my period which is when it hurts really bad. I am tired of hearing “we don’t know exactly what it is but I’m sure it was just a cyst, just start taking birth control to fix the issue”

Does anyone have any answers?