I Have A Rash On My Neck That Has Been

I have a rash on my neck that has been present for about a month and a half now. It flares up in the afternoon and becomes red and itchy. I had blood work done at my doctor's office and it didn't indicate anything. Any x-ray showed a sinus infection, but I have been on antibiotics for 12 days and still feel badly with cough, congestion and a productive cough.