Should I try different antibiotic while waiting for vet apt?

I'm not a vet, but if it were me, I'd continue with the antibiotic you are using and don't mix them. He's responding and giving another may cause a reaction. "If it works . . .", then call back and ask to see the newer vet so you can get in sooner. From our experience and our vet office, the newer ones have to confer with the senior vet, so you're going to get great care.