Without seeing the dog, it's impossible for us to determine whether or not he needs antibtioctics for a secondary infection. Good thing you are taking him to the vet!
edited to add: even if we did see the dog, without listening to his/her chest, we wouldn't know. The dog that I had was in severe distress (and if I remember right, had been seen by a vet several weeks earlier). It's nothing to mess around with.