Any advice on how to treat this

I'm 4 weeks postpartum, I started running a fever last night and it continued into today, not sure if this is what caused the fever. I noticed a bright red hot spot on one of my breasts. This is my fourth baby and I've never had this happen before so I'm not sure what to do. It doesn't feel hard or lumpy, just hot, red, and tender. Any advice? Thanks!