If you have a lump in your armpit after breastfeeding, you should apply hot compresses and local physical therapy to the affected area and massage the breast clockwise to promote milk discharge. If the symptoms continue without relief, acute mastitis can occur, which is an acute purulent infection of the breast tissue. In the early stage of infection, the breast is swollen and painful with increased local skin temperature, and the symptoms can be relieved by active anti-infective treatment with penicillin antibiotics. If the infection is further aggravated, a breast abscess may appear and often requires surgery, which is mostly done by incision and drainage of the breast abscess. All in all, if you have a lump in your breast, you should go to a regular hospital for breast surgery in a timely manner and undergo reasonable treatment under the assessment of a specialist. In daily life, you should also eat a light diet, avoid spicy and stimulating foods, and keep the milk ducts open to avoid milk stagnation.