Diagnose my dog?

[lizard]

This is a little lengthy, so I apologize and thank you in advance for reading.

So, my little mixed breed, 8 year old dog has been sick since the spring. One day I noticed his eyes looked kind of droopy and I thought he had had a seizure that we just weren't around for. Then he started vomitting a clear liquid.

We took him to the vet and they found he had pancreatitis, but that it was probably a secondary infection. He had an ultrasound and they thought he had IBS for dogs.

Fast forward to him continuing to vomit this clear fluid and declining rapidly, we took him to a new vet. I was sure we were going to have to put him to sleep. I was a mess. She put him on amoxicillin for 13 weeks and he was a new pup! We also switched his food to lo-res Iams wet food (we were feeding him a novel protein blue buffalo but it seemed to make him sicker). All of his symptoms disappeared.

We're now a couple of months since then and he's been regurgitating constantly so he's on three different antibiotics including a much higher dose of amoxicillin, but it doesn't seem to be doing the trick this time.

The vets really can't help us beyond scoping him, which would cost way too much. I'm worried he has cancer.

Anyone have anything similar happen to their dog? Or any advice beyond sticking it out with the antibiotics and hoping for the best? I hate seeing him so uncomfortable and sick.