Rash at the end of strep?

I was diagnosed with strep and a sinus infection a little more than a week ago and was started on amoxicillin. After a couple unsuccessful days of amoxicillin, was switched to Zpak. After THAT didn't work, I was switched to Allegra. Now I feel about the same with all my symptoms. Slight improvement with my throat and sinuses, but I have developed a nasty rash all over my body. Could this mean the end of my illness? Or will the rash stay for awhile?