My buddy's is ill and our small town very seems clueless.. Help!

So I've had my dog his whole life and in the past year he started throwing up once or twice a week. After the 3rd week or so we brought him in and they did like every test that you can get at a general vet done on him. Heartworm dyst. You name it.They can't find a issue with him. We have drawn blood. Done xrays . The works.. spent like $2000 in visits to the vet in the past year and no answers. The vet suggested that he could have a ulcer so we started giving him a ulcer med (which I didn't agree w cuz it was just a shot in the dark suggestion by the vet and my mom ran with it cuz she loves zukky to.. We all do.. And for about a month or so it seemed to stop .then it got worse. He can't hold a meal down almost every day he's throwing up. I have switched him in the past 3 days to a freeze dried expensive ass raw food. He absolutely loves it. But He is still throwing up. He seems super chipper still and happy and all that shit but then he'll just throw up and then lay around for a while but then he'll feel great again looks like so I don't know what to think. has anyone had an issue like this or does anyone have any opinions on what it could be. He's my best buddy I wanna be able to help him