Hi Kim,
I love this breed! Congratulations on your new family member. If you have not already done so, make sure you take a fecal sample into your vet for examination. The most common reason I see for soft stool/diarrhea in puppies is by far from intestinal parasites. Even if your little guy has received deworming medication already, he can still have intestinal parasites.
If parasites have been ruled out, then making sure you are adding a good probiotic to his diet (you can get one from your vet) will help re-establish normal bacterial populations in his intestines. If this does not make a significant difference, then I would start to suspect maldigestion/malabsorption problems, which can be genetic/congenital. To diagnose these, you vet will need to do several blood tests and possible biopsy his intestine. However, once you have a diagnosis, treatment can be started and is usually quite successful (although lifelong).
Please let me know how he does.......
Dr. Kris
Dog Veterinarian
Small Animal/Avian/Exotic Veterinarian for 16 years