From your history,,,seems like it can be a sebaceous cyst
A sebaceous cyst is a closed sac under the skin filled with a cheese-like or oily material.Sebaceous cysts most often arise from swollen hair follicles. Skin trauma
can also induce a cyst to form.These cysts are usually found on the face, neck, and trunk. They are usually slow- growing, painless, freely movable lumps beneath the skin. Occasionally, however, a cyst will become inflamed and tender.
But since now, it is persisting for quite a few months,, i would recommend that you visit a dermatologist
and get expert opinion,,,,,as any persistent swelling or lesion over the breast needs proper assessment by an expert...
Hope it helps
Dr Geetika Paul