[anonymous]

Has the dog had a senior workup? Labs? Neurology consult?
If not, that would be the only way to accurately diagnose him. Anything else is guesswork.
If it is not within your means, or you are not willing to have a complete workup $ done on an old dog.
Tell your vet, I mean you could spend a few hundred on x-rays and such only to be told he has an inoperable brain tumor (a cause of late in life canine seizures).
The other option would be to focus on care and comfort which may include anti-seizure medication, this may do the trick and keep your dog comfortable as it would stop the seizure activity. Read some of my prior posts in this thread. Good luck.
PS: I agree with your vet, I don’t think it’s his stomach (based on the info you have provided)
But, then again, sometimes they have more than one thing going on.
If your regular vet is willing to treat him for seizures (1 or more seizures per month) with medication, I would start there.