I hope your pup is better soon. I do know that it can take a long time to treat pneumonia, and a 'tracheal wash' with cultures can point you to the correct antibiotic if puppy doesn't improve. Years ago our young dog had pneumonia and we went through 3 antibiotics with poor success, the cultures showed an unusual organism and we switched antibiotics and he was on them for another 3 months but recovered and lived to be 15. If you are not comfortable with your vet, go to a specialty group for a second opinion. We often go straight to our local specialists, saves time and money in the long run.