[anonymously]

Try not to get discouraged, he is just a puppy, sometimes they stabilize and outgrow these things. My pet shop dog would have episodes of diarrhea, at least twice a week. This went on till she was 9 months old and then it just suddenly stopped!
I never even got it diagnosed and my other dogs didn’t get it……she remained healthy for many years, but then the big C took her.

Anyway, maybe get another vet’s opinion as SkeptVet suggested.