My cat has mouth sores/ulcers, tried everything. Any advice?

[BMan2016]

Hello, My poor cat, Bernie, is an indoor cat and over the past 3 months has developed terrible mouth sores on his upper lip. He also has sores on his stomach and bald spots where he continuously over licks himself. Anyone have any simple ideas? He REALLY hates getting shots and vaccines so that is not a road i want to go down. Any help is much appreciated!!!! Thanks.

Bernie's upper lip

DSCF2212.JPG (68.64 KiB) Viewed 276 times

[Mollycat]

I think this is a case for a vet really, at the very least for a diagnosis.

[BMan2016]

Well ......I left out a big chunk of backstory because we have tried the vet, steroid shots, allergic reaction tests, specialized dermatologist and spent plenty of money and seen no results. I am hoping someone out there has had a similar experience with there own cat and has some OTC medicine or
can think of something we are not thinking of that is causing this in our poor cat and how to address it. Thanks!!