Dysmenorrhea on the first day of menstruation is not necessarily caused by endometriosis. The majority of patients with dysmenorrhea experience more severe lower abdominal pain on the first day of menstruation. Endometriosis is not the only cause of dysmenorrhea, but also pelvic inflammatory disease and abnormal uterine development can cause dysmenorrhea. Due to individual differences, each person has a different degree of sensitivity to the pain caused by the contraction of the uterus caused by the prostaglandins secreted in the body, so the symptoms of dysmenorrhea are different. If you have pain in your stomach when you have your period, it is recommended that you have a detailed examination after your period clears to find out whether it is primary or secondary dysmenorrhea, and then give treatment.