Don't worry about the feeding for right now. They can go a LONG time without - as in months. And some do go off feed on their own without any negative effects.

Right now I'd focus on what the sore is. Unfortunately I have no idea what it could be. Try doing some digging, Googling, etc. on snake infections or sores, that sort of thing. Hopefully someone with more experience will jump in here!

Otherwise I'd advise a vet trip, to air on the safe side. But to an *experienced* snake and reptile vet! Not just any ole' vet.

Best of luck, and I hope things improve.