Pain during sex (week before period)

A week before my period starts I have severe pelvic pain with penetration. It's a sharp, stabbing pain that is deep and lasts anywhere from 30-60 minutes. The first day of my period I had sex again and there was no pain. Same with the week after my period is done. I have talked to my doctor about it and she ordered an ultrasound and the results were normal (no abnormal cysts). Just wondering if anyone has experienced this before? I am aware of endometriosis and educated about it, FYI, but of course have not been diagnosed. I am also not on birth control.