Sores inside mouth and under chin

Hi All, I have taken my cat to the vet 3 times, each time he has been given antibiotics and this almost completely disappears only to flare up even worse. In addition to what you can see in the photo, he also has sores in his mouth. Now they want to do about £300 worth of tests and then potentially remove his teeth. I really dont want this for my cat, its like de-clawing and I think its cruel so I thought I would do my own research to see if anyone has any ideas and if there is something I can do for him before he goes for his biopsy. He seems pretty happy despite this and is eating fine. 

Ooh, another possibly important bit of info, before this all started, he had terribly bad breath I just remembered!

Did the vet say anything about Eosinophilic granuloma complex or rodent ulcers? That's usually treated with steroids rather than antibiotics, though the article mentions antibiotics. Food allergies might be involved. One thing you could do in addition to what your vet prescribes is try giving fish oil as a supplement - normally a 500 mg. capsule squeezed over his food every day.

Oh poor muffin! I wonder if it's a rodent ulcer? Although I think your vet would've thought of that:
http://pets.webmd.com/cats/rodent-ulcers-cats

Or it could be an allergic reaction to the food he's eating, which is quite common. My friend's cat has recurring red lumps on his chin due to a food allergy.

I know that the idea of removing all his teeth seems drastic and cruel, but I have met a happy little cat who had all his teeth removed. He had a severe auto-immune disease that caused his body to attack his teeth. Poor little guy was so much better after all his teeth were out, and he gobbled up his meals no problem afterwards!

No, they didnt mention that, they seem to be rushing straight into expensive biopsies. I have been to 2 separate vets as well, have another appointment on Tuesday 

Has he had any symptoms of upper respiratory infection recently?
 

Nope

Do you have any photos of the sores inside his mouth?

Well, I took him to a different vet and he thinks its an allergy, put him on steroids and after 1 day, he is already looking a lot better so fingers crossed it clears up. Thanks for the tip!