If it is getting worse with the medication the vet gave you, I would guess that it is a burn. What is your set up like? What temperature is your heat mat? Do you use a thermostat for the heat mat?

I have never dealt with scale rot or burns but I would guess that that is a burn. I went to your gallery and saw the photo. I have an idea of what scale rot looks like, usually it looks really scabby, as a friend of mine has dealt with it a few times. I could be wrong, depending on how far along the wound is.