I wish you well and a speedy recovery. I got cellulitis and a staph infection after my surgery. The cellulitis appeared around the incision and was really hot and red. It was very painful and overall made my feel like I had the flu. I limped and was also swollen from the knee down. I had that typical flu feeling - that achey all over, crappy sort of feeling. I had a fever (which I did not know until I got to the doctor's office). They put me on antibiotics and it took a long time for the skin to heal. It is still dark but I did recover fully. The incision area cellulitis was a long time in healing. If you have a brace/boot then be careful as any skin irritation can cause the cellulitis to rear it's ugly head in that area.
AS I was told, cellulitis is an inflammatory response to an infection. I suppose your body was suffering inflammation in your urinary tract and was trying to telling you to get it checked out. Good luck and speedy recovery-