Hello Dear and thanks for the query
You need to be get properly examined by your gynecologist. Any bump on the breast is to be treated immediately as it appears because breast comprises of soft tissue
(fat) and infection spreads very quickly. In my opinion this bump could be a abscess
which can easily be treated with a course of effective antibiotic(s).
But it should be done as early as possible. Consult your doctor and get treated by finding out the cause. Do not hesitate to go for investigation like sonography