If it's truly the tooth it would need to go or the infection won't clear up. If there's necrofying tissue in there, it will keep on creating infection in the abcess. Once the tooth is pulled and the infection can drain, antibiotics can clear things up pretty well.
When I have been told to give penicillin it's for 7-10 days, he's not going to be liking you much on the 10th day. He's going to get real unhappy in about 3 days I bet. Bute is either for pain, inflammation or fever, so I wouldn't give the bute unless he's showing signs of pain or has a fever, you can cause ulcers by giving too much bute.
Is there another vet you can use?