Holding head up, yawning, and mucous are ALL classic signs of respiratory infection. Sounds rather advanced, and it WILL kill a snake. You need to get it to a vet as soon as possible. Make sure your temps are spot on if not a LITTLE bit high, and that your humidity is around 60-70% as well.

As far as the black spots, they could be mites. See if you can remove one with a q-tip and take a look under a magnifying glass. If its a bug, chances are its mites.

The symptoms you described, though, are from the RI and it needs to be treated NOW.

Steve