I had the same problem with Jojo i was keeping the humidity too high. Unknown to me my digital hygrometer\thermometer was malfunctioning and was giving me false readings. It was telling me it was warmer then it was and that it was more humid then it really was. Go to the vet its not something that will just go away it has to be treated with a fungicide. After about a week the sore will go away and will be gone in the next shed. Good luck and welcome to the best dang Ball Python forum in the world.