The presence of brown discharge four days after menstruation is considered to be due to a number of factors: 1. The presence of gynecological diseases, such as endometrial polyps, submucosal fibroids, and even cervical canal polyps, can also cause brown discharge. 2. Inflammation of the vagina, including cervical inflammation, is related to the inflammation of the cervix, which can cause abnormal bleeding during activity. It can also be due to human papillomavirus infection, causing contact bleeding. 3, to rule out the existence of ovulatory bleeding, because some women ovulate early, due to the rise and fall of hormone levels, can also produce the phenomenon of endothelial rupture, so there is brown discharge. You need to go to the hospital for an ultrasound examination to determine what causes the bleeding, and depending on the situation, you can take oral anti-inflammatory and hemostatic drugs for treatment.