Does your snake have a rock in its cage? There is a chance that he is trying to get under the rock and damaging the skin on the top of his head. If so, I'd take the rock out.
Shotgun treatment for skin problems is to first check over the basic husbandry, such as cleaning, humidity, and temperature. Clean the cage and put in newspaper so that the cage is dry. Moisture favors germ growth. Then get a tube of Betadine cream. It's a first aid cream available over the counter in many drugstores. Apply some to the affected area every day. And ultraviolet light is hard on many microorganisms, so taking the snake outside for around 5 minutes every day so that unfiltered sunlight gets to the affected area may help, too. This may not be possible though. Continue treatment with the Betadine through shedding time and repeat it once or twice after the shed. You can raise the humidity at shedding time. Then watch the spot to see if it is better. Abraded skin may take several sheds to fully heal, if that is the problem. Skin diseases clear up faster than that, usually. Good luck.