hi..thanks for the query..
I would first suggest you to try and find out the cause of the blisters before treating only the superimposed infection.there is a variety of blistering disorders of the skin. The diagnosis is based on physical examination and a biopsy
of the fresh blisters( not the infected one ,as they are now.)Hence try to complete the course of the oral antibiotic and get the appropriate diagnosis with a dermatologist
for the itching, you can have oral anti histaminics..they are very helpful to relieve the itching.if you are sensitive to topicals ,it is the best to stay away.
There is a possibility of an eczematous rash
as well , if the size of blisters are small.
Hope this helps.take care!