I'd suggest having your vet check the pup for a digestive problem seen in this breed called pancreatic insufficiency which you can read about here
But only if you have already ruled out giardia or coccidia infections.
For that a really fresh stool sample can be checked by your vet. Your pup may need meds or supplements to get over this.
A really digestable food such as California Natural or an alternative diet such as Wellness fish and potato might work for him if its a food sensitivity issue.
You can read about inflammatory bowel here
Hope this helps you!
OK then next step would be a check for intestinal parasites such as worms (see links for info)
And usually a very fresh stool sample is all that you need to bring to the vet to get the pup checked for those.
If that isn't it then the vet would do a blood work test for the pancreas issue.
If you read the first link in the above answer on the pancreas issue it says in part
"In some instances, raw pig pancreas can be used. The pancreas needs to come from animals certified as healthy by an approved meat inspector. Accurate dosing is more difficult with the raw pancreas, but in general, a 45-pound dog would need to receive 3 to 4 ounces of the chopped pancreas. The raw pancreas can be frozen at -4ºF for up to 3 months and still retain its enzyme activity."
But the problem may be parasites and curable by use of the meds for whichever parasites show up.