Those are actually very helpful pictures. I had a leucistic Texas rat snake with a similar problem on the bottom side of his throat. To me the yellowish tissue on your snake's bottom jaw looks like some kind of erosion, rot, or infection. I would guess that he was perhaps in too humid an environment or obtained an injury that went untreated and became infected. That is just my best guess though. Perhaps try a topical antibiotic until you can get a vet to take a look at it?