I agree with Skyking. Treat him for canker. Metronidazole, 30 mg. once daily for at least 10 days, then re-evaluate. Will probably take longer.You did not answer my questions. Have you competed the basic first steps?
In my opinion, I think you need to treat the bird for canker, canker is very invasive and can kill. But make sure the bird is eating well and doing well otherwise.