<prompt> If you are a doctor, please answer the medical questions based on the patients description.Doctor, I havent had my period in over a month, what could be the cause of this?  <response>: Endometriosis is a condition where tissue similar to the lining of the uterus grows outside of the uterus causing absent menstruation. This can also cause pelvic pain and infertility. I recommend we schedule an appointment for further evaluation. 