The stomach distension and lumbar pain after menstruation may be a normal physiological phenomenon, or it may be caused by urinary stones, urinary tract infection, gynecological inflammation, gynecological tumors and other reasons. 1. Normal physiological phenomenon: after menstruation, the hormone level in the female organism returns to normal, the endometrium is gradually repaired, during the recovery period, it may cause stomach distension, back pain. 2. Urinary stones: for example, bladder stones, bladder stones after menstruation, due to stone stimulation, will cause stomach distension and lumbar pain symptoms, may also be accompanied by urinary difficulties, frequent urination and other symptoms. 3. Urinary system infections: for example, pyelonephritis, there will be symptoms of stomach distension and waist pain, which may be accompanied by fever, fatigue, hematuria and other symptoms. 4. Gynecological inflammation: commonly seen in cervicitis, pelvic inflammatory disease, under the stimulation of inflammation, resulting in pelvic or cervical local mucous membrane congestion and edema, may cause stomach distension, accompanied by symptoms of lumbar pain. 5. Gynecological tumor: for example, endometrial cancer, cervical cancer, etc., after menstruation, the symptoms of stomach distension and waist pain may occur frequently, which may be accompanied by irregular vaginal bleeding. There may be other reasons for stomach distension and lumbar pain after menstruation. If the symptoms continue to be unrelieved, or if the symptoms are serious, you should consult a doctor as soon as possible to diagnose the cause of the disease, and then be guided by the doctor to carry out the treatment and regulate the disease.