Aww poor baby, I hope he feels better soon!! Have you tried some boiled chicken and rice, that sometimes helps with upset tummies..Peanut was on NB Potato and Duck and then I found innova evo red meat small bites so I started him on that, I didnt mix it or anything I just gave him his new evo food, he didnt have any type of reaction to the new switch and he is doing great on it
I love that food!! When he is sick like that I would just try the boiled chicken and rice- really bland, till he gets better or you can also give him some keaopectate..( i cant spell it) that helps too, you can get it at like cvs or walgreens
good luck