Should I try different antibiotic while waiting for vet apt?

Stay with the amoxicillin and don't worry about getting an earlier appt AS LONG AS things don't get worse. It sounds like you've made great progress thus far. That smaller abscess may still need to be treated with a drain/flush procedure but that's a decision your vet will make.

There is no hard and fast rule about max length of treatment with amoxi.

Doug, DVM