Ooooh ... Cellulitis - that brings back a painful memory.
Approx 20 years ago, I had the misfortune of having this, somewhere around my shin. I remember it being extremely painful - I had to elevate my leg to help alleviate the pain.
I was given a course of antibiotics, these had no effect. The rash got worse and I was admitted to hospital and put on a drip for 10 days. Thankfully the drip worked and I was discharged from the hospital. Whilst I was in there, 2 other people were admitted to the same ward as me, with cellulitis. The first had it on his hand and had to have the "boil" lanced as it had gone too far and the 2nd had it on his foot and had to have his toe amputated as that had gone even further.
Anyway, I'm not trying to scare you; these were rare cases - antibiotics usually work .... I feel your pain and I hope you recover quickly :)