My Peaches (Shep/Chow X) used to go through something similar - what I wound up calling Shepherd Stomach. Our vet couldn't find anything, so I changed her food (removed poultry entirely) by switching to Solid Gold WK and she's been fabulous ever since. I do monitor her treats as well, since she's a particularly sensitive dog, and too many of any one type just don't sit well with her. Good luck with Buster, I hope he feels better soon, and you get some rest (nothing like *that* noise to wake you from a dead sleep
)