The pain on the left side of the left breast in breastfeeding patients may be due to milk stagnation or inflammation of the breast, and it is recommended to go to the hospital for examination to be able to make a clear diagnosis, as follows: 1. Milk stagnation: it can lead to local hard nodes, hard lumps, and also some pain. 2. Inflammation of the breast: it is usually secondary to milk stagnation on top of bacterial infection in the breast, and the condition will further aggravate, such as Local hard nodes, pain is very obvious, there is obvious pressure pain or tenderness, there may even be throbbing pain, the patient will have fever and other phenomena, an ultrasound examination will be able to make a clear diagnosis. For symptoms caused by milk stagnation, methods such as massage and lactation are usually recommended, and for symptoms caused by breast inflammation, antibiotic anti-infection treatment is usually required.