It sounds as if your dog keeps building up a resistance to the antibiotics.
However, I would ask your vet before "hitting him up" with anything. It is illegal for your friend to administer any prescription drugs to your dog (breeder or not) unless they are a DVM. Ask your vet, if your vet okays it, then it's atleast "above board".
What if your dog is allergic to penicillin? Then what?
1.5cc could indicate the use of a needle. Very dangerous if someone doesn't know how to give a IM injection. Or is it oral penicillin?
Maybe someone on this site can offer you an alternative remedy -Luba?