What Causes A Itchy Rash On The Vagina?

i developed a itchy rash on my vagina, no discharge, no smell. Tried all kinds of products o noavail. Went to OBGYN she said definitely was yeast put me on ceam a two pills. It was gone in 24 hrs. About that time she called and said my cultures were growing clostridium so ordered Flagyl....well now I appear to have it again from the antibiotic? Yeast? I thought from my microbiology days clostridium was what caused botulism. How did I get it in my vagina?