Isolate his enclosure in a separate room from any other snakes you have so they don't get sick. He should be in a minimalistic setup - paper, plastic hides, water bowl - the same as a QT enclosure so you can clean and disinfect it daily. If he was on wood/aspen substrate in his old enclosure then throw away the substrate, and thoroughly clean and disinfect everything else that was in it.
Bump up his temps and humidity.
Vet appointment ASAP.