Lumps in the armpits during breastfeeding may be caused by lymphadenitis and mastitis, and can be taken orally with erythromycin and amoxicillin; they may also be caused by sebaceous cysts, which need to be surgically removed if the cysts are large. 1. Lymphadenitis, mastitis: armpit lumps, with redness, swelling, pain and other conditions, considering the inflammation, may be lymphadenitis, mastitis, etc., can take antibiotics such as amoxicillin, erythromycin and other oral medicines. 2. Sebaceous cysts: they are caused by the blockage of sebaceous gland ducts in the axillary skin and the accumulation of secretions, which can also lead to the phenomenon of pimples. The main focus is on surgery, through which the cyst can be cut open to remove the swelling; at the same time, erythromycin ointment or mupirocin ointment can be applied to prevent infection. There may be other reasons for breastfeeding underarm bumps, and safer drugs need to be chosen. It is recommended that the patient go to the hospital to get a clear picture of the cause and follow the doctor’s instructions, do not blindly use medication on your own.