Dog has diarrhea once a day

Hi i have a lab/pit mix and lately he has been having diarrhea/loose stool about once a dat. He has always had a very sensitive stomach so i am assuming it is just that. He'll have one solid poop in the morning then i will feed him (prescription food for his sensitive stomach) and then around 4 hours later is when the loose stool comes. He has been acting completely normal.

Going to start him on some pumpkin today, gave him some plain greek yogurt yesterday to try and get some good bacteria in his stomach.

Anyone have any other recommendations or deal with reallly really sensitive bellies?