If you have sex during menstruation and have pain in your stomach after reaching orgasm, the following causes are common in clinical practice: First, the uterus contracts due to sexual stimulation, and menstrual blood in the uterine cavity may flow into the pelvis along the fallopian tubes. The blood enters the pelvic cavity and stimulates the pelvic tissue causing pain in the lower abdomen. Secondly, the relatively rough action of sexual intercourse can stimulate the uterus to have uncoordinated contractions, which can also cause pain in the lower abdomen clinically. It is recommended not to have intercourse during menstruation because it can cause inflammatory reactions in the reproductive tract, which can also cause the possibility of endometriosis, which is very dangerous and not good for women’s health, so special attention should be given.