Could be cellulitis, a serious infection of the skin. (I had one on my leg last winter.) A week's worth of antibiotics fixed me right up. But don't fool around, get seen for this right away! It can easily progress to sepsis, an infection of the blood!
I felt foolish going to the ER for what I thought was just some kind of rash. (I have no family doctor) But they took it quite seriously at the hospital. Go now!
