It could be a bacterial superinfection. I'm a nurse and bacteria in the poop has a distinct smell (very nasty even I gag). So does blood in stool. Blood smells so nasty. I'm sure you brought this up to the vet? What did she say to do? What was his original diagnosis? Food definately could do it but it shouldn't be that untolerable. Try changing the litter more often. Do you have a weak stomach to smells as it is? Let us know the anaswer would help big time.