Breast pain a week after menstruation may be caused by physiological factors, endocrine disorders, breast hyperplasia, mastitis and other factors. 1. Physiological factors: for example, girls in puberty or wearing a bra too tight, causing pressure on the breasts, can cause physiological breast swelling. 2. Endocrine disorders: polycystic ovary syndrome, pituitary tumors and other factors may lead to endocrine disorders, which may cause breast swelling and pain in non-menstrual periods, and may also cause menstrual cycle disorders, excessive or low menstrual flow and other abnormal manifestations. 3. Breast Hyperplasia: It may be related to long time drinking and smoking, excessive mental stress and other factors, which can lead to a continuous increase in the level of hormones in the body, which can stimulate the mammary glands and cause breast hyperplasia, which in turn leads to breast swelling and pain, and when touching the breasts with your hands, you can touch the soft lumps. 4. Mastitis: It may be related to milk stagnation or bacterial infection, due to breast stimulation, there may be symptoms of breast swelling and pain, which may also be accompanied by fever and fatigue. If your breasts are swollen and painful for a week after your period is over and physiological factors are ruled out, it is recommended that you seek medical attention for the appropriate examination and treatment.