Has he been given a round of Baytril? Did that help at all? Otherwise you might want to look into clostridium infections and treating with Tylan powder. Payton was on round after round of Baytril, and the diarrhea cleared up WHILE he was on it - but immediately after he came off it he went right back to being sick. The Tylan powder was the only thing that actually got him healed up.
My parents were about ready to kill him because he was having diarrhea all over the house because he couldn't hold it (it was THAT kind of diarrhea, not just loose stool) and my parents just looooooove carpet. Light-coloured carpet. And that's nothing to speak of the 2AM my puppy just crapped all over my bedroom so I'm cleaning the floor and giving the puppy a bath occurrences... yeah. It's not pleasant. =<
Reportedly Baytril can help SOME colstridium infections, but it didn't work for Payton's obviously. If you haven't gotten an RX for it yet, definitely give it a shot and see if it helps any. You have to buy a whole bucket of Tylan powder and it's like $40, and you'll use quite a bit, but definitely not all of it.