You should start noticing a difference within about 24 hours of taking the first antibiotic. I developed mastitis in my cancer breast about 10 days in to my radiation, felt rotten, high fever, breast didn't turn red for about anothef 24 hours. As with @Afraser, turned out to be from a persistent seroma. Completing radiation 4 weeks later was such a relief. In spite of developng breast lymphoedema in addition to arm lymphoedema, I haven't had another infection yet, touch wood (2 years since radiotherapy finished)
Get well soon
Lyn