I see that this is from a couple weeks ago, but I thought I'd share my experience.
With DS1 I had one early case of mastatis when DS1 was 3 weeks. Antibiotics cleared it up really quick. Then I also got it when DS was about 14 months (yes, over a year!) Which was such a surprise. That time I managed to get rid of it without antibiotics. I left work early due to the fever, took a bunch of ibuprofen, pumped as much out of the breast as possible while really massaging the lump. I think the ibuprofen is key here, since massaging in itself can cause more inflammation that could prevent clearing the blocked duct, but the ibuprofen, being an anti inflammatory, help counteract that. I then got in bed, piled on th blanket, and slept for ever. That killed the fever. My immune system was able to deal with it, but only because I was able to get the rest.
With DS2, now 5 weeks, I've had the beginnings of mastitis twice. On both opposite breasts. Tender blocked ducts, small read patches visible on breast, feeling under the weather. Both times I as able to get rid of it with out antibiotics (just ibuprofin, firm breast massage, and as much rest as possible). I think the key for me in treating on my own was knowing the symptoms and working to resolve it as quick as possible before the infection get too established. But of course rest is key too...if you're only sleeping 2 hours a night, your immune system is shot. I've been lucky that DS2 has allowed me a 4 hour stretch of sleep most night (dS1 never did at this age) Im sure that's helped.