sorry ur little fellow is not well and i am sure for your it is also nerve wrecking experience with ur little one...just a suggestion incase it has been over looked but could it be irritated bowel syndrome or colitis due to stress as u mentioned it seemed to subside some with the predisone...
here are a few links to read about it:
Inflammatory Bowel Disease IBS IBD in Dogs and Cats Colitis, Inflammatory Bowel Disease and Constipation in the Dog and Cat at ThePetCenter.com Dog Colitis | Largest Pet Health and Medicine Information Dog Colitis | DogTime
I have seen similar in a dog a friend was bby sitting and he had colitis ...did not want to go and when he did it was water with a little poopie and painful too wimpering when he went ...u may consider a little teaspoon of yogurt daily as a treat and also a small piece of bran bread about a 1/2 inch square ...it did help that dog !
wish you and ur little fellow a healthy outcome
