What is wrong with my Ball Python?

Underlying skin disorders like scale rot, dermatitis and necrosis are caused by bacterias or, a fungus. A moist moldy enclosure is a breeding ground for these organisms. When a snake is in shed, it's entire belly turns pinkish so, the shed scenario could be ruled out. It may be best to have a vet treat him. Till you can get him to a vet, apply some Neosporin to the affected areas and keep him dry like you are doing right now.