Palpation. Some lumps are 'typical'. Others can be sinister. However, it is wise to consider removal at your leisure: my Surgeon told me that no healthy breast has a lump. Mine, when sent to histology, had 'changes' when excised, which could have been slow growing but we will never know.
Masititis can come and go and is intensely painful. Mum developed breast cysts if she ate shell-fish, within 4-5 weeks. So she now avoids it. They even have a chart on the kitchen wall to alert staff of her allergy. Each was removed and looked at. Her lump that was cancerous was found on mammogram at 65, it was obvious on film.
Maybe discuss with a Surgeon - take a list of concerns with you. Might be wise to have a follow-up in 4-6 months to put your mind at rest.