auntypebbles,
Unfortunatly I hear about these type of situations all to often and it sickens me. People are misdiagnosed every day. I was one of them ten years ago. I know what you are going through and I don't like when others have to go through it.
Soooo... The following is what I would do.
The first thing I have to say is that he needs a new doctor now.
Secondly, whether medicare covers it or not, he needs to have a biopsy.
Recurrent ulcers in the same spot, painless or not, need to be investigated. Mouth ulcers that are innocent disappear and completely heal in 10-14 days. They can be very painful and cause lymphnodes to enlarge but everything returns to normal when they heal. They also do not usually continue to appear in the same place unless there is and associated irritation.
In my opinion, he needs to immediatly see an ENT or Oral surgeon. Find a doctor or for that matter a dentist who will refer him.
Good luck.
My thoughts and prayers are with you both.
Cheers,
Mike