Mastitis, breast hyperplasia and breast cancer are common causes of hard lumps in the breasts after menstruation, and different treatments are needed according to the causes. 1. Mastitis: It usually manifests as swelling, redness and fever in the breast. In this case, oral cefdinir and levofloxacin can be used for treatment. 2. Breast Hyperplasia: Lumps caused by breast hyperplasia nodules are more common, accompanied by pain or tenderness, which decrease or increase cyclically with menstrual changes. It can be treated with oral treatment under the guidance of professional doctors. 3. Breast Cancer: Early breast cancer is usually painless, while advanced breast cancer will show symptoms of pain and hard lumps. Generally, radical breast cancer surgery is needed. When patients have hard lumps in their breasts after menstruation, they should go to regular hospitals for examination as soon as possible and under the guidance of professional doctors for treatment.