Sounds like a respiratory infection to me.

Do you have photos of your setup? What are your temps? Humidity? What do you use for a heat source? What are your hides like? What do you house the snake in?

Go to a vet as soon as you can, a respiratory infection can kill your snake quickly. Reptiles go down hill very quickly once they have a sickness, so you do not want your snake to die.

For an estimate of what the bill will cost, around $100. But every vet is different.

If you own any other snake, reptile, or amphibian, please take your sick snake to a different room in the house to keep it away from your others. The others can get sick easily from being exposed to this sick snake in the same room. You may want to check the others for any respiratory problems, AFTER you wash your hands thoroughly.