Being that your puppy is young. I would put a sample in the ziplock bag and take it to the vet for a quick fecal check.
If that is negative you have a few things to consider. The food the Cairn is eating, whatelse the puppy has ingested, etc. I am not fond of giving these little guys anything for diarrhea until you figure out a cause. The puppy shouldn't be eating rawhides or pig ears or dog treats, their intestinal tracts are very sensitive...just like human babies. It should be strict puppy food and puppy treats.
Good Luck,
Dr.V
Dr. D.A. Vamvakias
Veterinarian