Hi, Can't give any clinical expertise however our pup (now a year old) has had a long run of issues with dodgy tummy!
It all started when he was around 16 weeks old, he started having really loose poos and 'scooting' as if he was in discomfort.
As first time owners we ofcourse panicked and took him to the vets time and time again, we kept him on wainwrights kibble, cut out wet food and for a short while he was fine (at this point he was on turkey and rice) . A couple of months later the issues started all over again. We switched him to salmon and potatoes kibble and it all began to sort itself out. For a couple of months we kept him strictly on salmon and potatoe. No chews, no treats etc kibble was used as his training treat.
We are now at 13 months old and for the last month i have been introducing him to more and more meats etc to test his stomach as thus far, the only thing he has had a bad reaction to is chicken or turkey. Everything else has been absolutely fine .
We are even at the point now where sometimes he seems constipated.. And therefore I give him something that I know will 'relieve' him
I guess what I'm trying to say is from my experience don't panic too much.. I was so worried that my dog was allergic to everything and I would end up spending thousands on special diets etc but it has all worked out fine