I'm so sorry you are going thru this. Why wouldn't your old vet try to figure out what had caused the bumps instead of just sending you home with some multi-ppurpose drugs. If the bumps are pus filled, then there is an infection. So what is causing the infection???
I think I'd see a different vet. I hate when vets (or dr's for that matter) say "I don't know what it is, but take this.") DUH. If you don't know what it is, then why prescribe something that might not work. In the mean time, the patient (fur or skin) may suffer even more if the meds don't work. Sorry, it makes me mad and it happens all the time. There may be something you can do to take care of it on you own or even keep it from happening if the vet would try to find out what it is. Again, I'd ask a different vet. Good luck. I hope this one can do the right thing and I hope Oliver starts feeling better.