Marisa is correct, the snake needs to see a vet. Not because people here are unwilling to dispense helpful advice, but because it sounds like the snake is in an advanced state of Respiratory Infection and there is not much we can offer. Since snakes really only have one functional lung (the other is a vestige and very small) an infection is very serious and the snake sounds to be past the point where a simple change in temps and humidity would clear it up. You need to see the vet and get Amikacin/Amiglyde (broad-spectrum antibiotic) injections as I see this to be the only way to clear up the infection.
Good Luck, keep us updated...