Did you go to a cat/dog vet or a vet that is experienced with reptiles?

To not be able to diagnose the problem and say that "it might be IBD" sounds to me like the vet just didn't know what he was doing and trying to save face. IBD makes quick work of ball pythons and if your snake actually had it, it would be dead by now, and your other pythons would probably be beginning to show symptoms as well.

I'd find another vet...