Small stomach pain after sex may be caused by uterine contraction, pelvic inflammatory disease, endometriosis and other reasons. 1. Uterine contraction: when having sex, stimulation of the cervix may cause uterine contraction, resulting in a vague pain and discomfort in the lower abdomen similar to menstruation, which can disappear after a period of time. 2. Pelvic inflammatory disease: when there is inflammation in the pelvis, when having sex, due to the stimulation of the pelvic cavity, the pelvic cavity congestion leads to inflammation aggravation, so there will be the phenomenon of pain in the stomach after sex. 3. endometriosis: some patients with endometriosis, due to endometriosis nodules in the pelvis, touching the endometriosis nodules during intercourse, there will also be the phenomenon of pain in the stomach after intercourse. The symptoms of small stomach pain after sex, the patient should promptly go to the hospital for treatment, to clarify the cause of the disease, and regulate under the guidance of the doctor.