Stomach pain on the third day after intercourse is considered to be caused by pelvic inflammatory disease, luteal rupture, uterine fibroids and other diseases. 1. Pelvic inflammatory disease: Pelvic inflammatory disease is a common infectious disease of the upper reproductive tract in women, and patients will experience symptoms such as lower abdominal pain, fever, and increased vaginal discharge. The cause of the disease is related to pathogen infection, and the triggering factors include sexual activity, lower genital tract infection, etc. Some patients will have stomach pain on the third day after coitus. 2. Luteal rupture: Luteal rupture is related to the formation of luteal cysts, coagulation dysfunction and other factors, after sexual intercourse, trauma and other abdominal pressure, the patient will experience abdominal pain, internal bleeding, vaginal bleeding and other symptoms, and in severe cases, shock can occur. 3. Uterine fibroids: uterine fibroids are tumors formed by proliferation of uterine smooth muscle tissues, the cause of which has not been clearly defined and is mostly related to heredity, hormone and other factors. Typical symptoms of patients are abnormal menstruation, abnormal vaginal secretions and discomfort in the lower abdomen, etc. Some patients may also experience stomach pain on the third day after intercourse. There are many reasons for stomach pain on the third day after coitus, so it is recommended that patients go to the hospital in time for relevant examinations.