This could be an infected cyst,or maybe an abscess that can occur on the breast like on any other part on the body.These kind of infected lumps can be lanced and drained.But if it keeps coming back,surgical removal of the infected area may be necessary.Has your doctor made a culture of the infecting organism? If not,then it should be done so that a proper antibiotic treatment can be focused on the offending organism.It is also possible that your infection keeps coming back because you may have some other illness which could affect your immune system, like for example diabetes.
Depending on the cause,it is important to follow your treatment plan to ensure that you are completely rid of both the infection and any primary disorder that may have caused it.
I would,if I were you, seek medical evaluation preferably by a breast specialist who may want to conduct a few tests for a complete check-up.
I don't think you should be worrying too much about it ,because it doesn't sound at all like a breast cancer symptom.
I hope your problem will be resolved soon.
All the best.... :)