Vet time! Get a fecal float done.

I'm guessing that, due to some form of husbandry issue with the previous owner, whether it be too cool basking temps or some more complicated health problem, the snake initially regurged while at its previous home. Then, as others have said, the digestive distress causes him to have trouble keeping food down, even when husbandry is corrected. I normally give adult snakes 1 to 2 months without food to let their digestive systems recover, but it sounds like even one month might be pushing it for your little guy.