fat necrosis, inflammation, abscess, infection, no idea why?!

cityrat

After finding a big lump with tenderness and some swelling (everyone's sure not IBC) and having mammo and US, and biopsy, the following was reported:

"Fat necrosis with many Gram-positive cocci in clusters, extensive granulomatous acute and chronic inflammation with abscess formation, histiocytic reaction and stromal fibrosis. Adjacent scanty unremarkable breast parenchyma. No atypia or carcinoma identified.

Note: Seciton shows extensive acute and chronic granulomatous inflammation with scanty breast parenchyma seen in the background. Pancytokeratin is negative for carcinoma. GMS and Gram stains highlight many clusters of cocci. Acid-Fast Bacilli (AFB) stain are negative for organism. Please refer to right breast wound culture results for details of the bacteria. Overall, the etiology of the changes is unclear, with differential diagnosis including granulmatous lobular mastitis, infectious disease and reactive changes to yet identified process, among others. Clinical and the radiology correlation is recommended. Case also reviewed by another beast pathologist. "

No idea what this is and nervous. I've been given antibiotics and told to come back for another ultrasound in 2 weeks and a follow up visit. I'm small-breasted so she doesnt want to make a "dent" from excision if it goes away on its own. But if it doesn't, what could it be? I've been on the antibiotics for 2 days now and it hasnt really gone much smaller. I have had no local injury that i can think of, am not breastfeeding. I'm 51 and at peri/menopause and taking low dose b/c pills for that. everyone seems a little baffled. Any clues?