[BellaDonna]

Is it possibly poop matted in the hair tht is blocking his rectum? I had that happen once with an outside cat because he had runny stool, I didn't know it and it built up on the hair and virtually didn't allow him to poop. I had to catch him and clip and soak it off. He must have been in such pain. He had tried so hard his rectum was pooching. Thankfully once I caught it and medicated him he cleared up.
Another thing could be somthing ingested that he is having trouble expelling. How did you end up bringing home a 6 week old puppy??? I think that is way to young for a Yorkie pup to leave mom.