There are many causes of menstruation coming back after a few days, such as ovulation bleeding or episodic ovulation bleeding, vaginal or cervical lesions, inflammation of the reproductive tract, endocrine disorders and so on. 1. Ovulation bleeding or episodic ovulation bleeding: bleeding occurs one week after the end of menstruation, and the amount of bleeding is relatively small, which is related to the fluctuation of estrogen level in women’s bodies, and generally does not require special intervention. Continuous ovulation bleeding needs to be alerted and other pathologies need to be ruled out. 2. Vaginal or cervical lesions: If abnormal bleeding occurs after intercourse, cervical polyps, cervical intraepithelial neoplasia or tumors may be considered. 3. Inflammation of the reproductive tract: If vaginal bleeding is accompanied by abdominal pain and increased secretion, inflammation of the reproductive tract may be considered. 4. Endocrine disorders: If the bleeding is prolonged and heavy and there are no other special symptoms, endocrine disorders can be considered. When patients have this situation, they need to do gynecological examination to observe the bleeding site. It is also necessary to do ultrasound to observe whether there are organic lesions. Based on these two examinations, further tests will be done to clarify the diagnosis.