stick to what works even if a vet food and he has to be on it for life - if they suspect ibd which i kind of suspect as they vomit food up sounds like small intestinal issue and could have been from the worming stuff maybe might have messed up intestinal tract a little bit so you need to calm it down and that can take time with ibd or colitis dogs - if you have a food he can keep down from vet stick to it - it could take 30 days to calm an inflamed intestinal tract down. it took my dd 30 days of soaked food after a metacam incident that triggered colitis in her entire intestinal tract and then i tried chicken and rice and it made it worse as ibd dogs sometimes cannot tolerate chicken as ibd is a food intolerance.
so please stick to what works and what he will it and if that is i/d then stick to it or you could risk him getting something like pancreatitis bc if the small intestines backs up and he keeps having issues that can trigger the pancreas since they are right next to each other and pancreatitis runs in this breed. I am not a big fan of i/d and would say to check with vet about ultra z/d even though it is chicken it is a hydrolized diet where protein is further broken down and it works well with ibd and pancreatitis dogs. The i/d has pork in it and since my dog relapsed on it with pancreatitis that food makes me nervous.
my dexter has ibd in small intestines and it triggered pancreas so he had pancreatitis a couple times
not fun so i know your frustration - hang in there