Thanks Nicole...I will ask the vet about Tylan.
Well I took him to the vet and just got back the results of his stool test...negative.

But like I read in my search, it could still be worms but not showing up in his poops. I guess I'll have to talk to the vet and find out if he feels a de-worming would be worth a shot, or if we should just try the Tylan.
I put him on a diet of rice and boiled chicken for a few days to see if it settles his tummy. He's got TONS more energy, but the poops are still runny - all that changed was the color (they're very pale now).
Don'cha just love the graphic poop talk?