Hello There. I can understand your concern. is there any pain in the swelling? have you noticed any change in the site or size of the swelling? if there any relation between the menstrual cycle and the swelling? it could just be a fibroadenoma. kindly get it checked out by a general surgeon. a test called mammography would be necessary for this condition which will be prescribed by the surgeon itself. best regards, Dr. Anil kumar jain