The left side of the chest pain is considered to be caused by the following conditions: first, it may be caused by trauma to the left side of the chest. Secondly, there may be breast enlargement on the left side of the chest. Breast enlargement is mostly related to the patient’s endocrine abnormality, which may result in the symptoms of lump in the breast and breast pain. Especially during ovulation, before the onset of menstruation, when angry and when tired, the symptoms will be more obvious. Thirdly, if you are breastfeeding at this time, you should consider the inflammation of the mammary gland caused by the accumulation of milk in the right breast, which may cause hard lumps, pain and redness in the breast. Fourth, the pain may be caused by the increased secretion of estrogen and progesterone in the body after pregnancy. It may also be caused by pubertal development or diseases such as pleurisy. It is best to go to a hospital breast specialist for further consultation and treatment. Fifth, and most importantly, be sure to pay attention to angina pectoris or lung infections and tumors.