Breast enlargement can cause axillary pain, the underlying cause of which is painful discomfort due to impaired lymphatic return to the axilla caused by breast enlargement and subsequent reactive enlargement of the axillary lymph nodes. It is usually due to reactive inflammation of the axillary lymph nodes and not a bacterial infection.
Breast pain is relatively pronounced in the pre-menstrual period when one is prone to anger and depression. Its pain is mainly tingling, vague and swelling. Some have parametrial tissue in the armpit, which can also be the cause of armpit pain.