Full anal glands. Max had this problem once when he was a pup when the vet took a manual stool sample. Did the vet do this today or take a rectal temp?
Hate to say it, but I would have the vet take a look. I would be too nervous to try to express glands on my own. Too much can go wrong if you are not experienced.
I have to admit, seeing puppy Max do the scoot was hilarious, like he was rowing a boat.
