Hi,
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 are usually treated with antibiotics.But if it keeps coming back,surgical removal of the infected area may be necessary.
I don't think you should be worrying too much,because it doesn't sound at all like a breast cancer symptom,but you should see your doctor ASAP so that this painful lump can be adequately treated.
Best wishes...
I forgot to mention I cant see it but I can sure feel it