BTW, from everything you've posted about him, I don't think a vet visit would be of any help- this is very likely a husbandry issue that's entirely fixable by you. In fact, vet visits add a lot of stress, so it can actually be counter-productive for a fearful snake, which yours is.
Fix his home, & don't handle him until he has eaten at least 3 times at reasonable intervals without refusals (unless in shed- snakes normally refuse food when in shed cycle). Being handled inhibits a snake's appetite- so right now, he's in fear mode.
And since he came from a breeder, the other thing that would have helped him to make a smooth transition for you is IF you had duplicated exactly how he was kept by the breeder, instead of planting him in a 20L tank, especially one without proper 'hides'. Most likely Wilbanks kept him in a much smaller, cozier tub.
But avoid making lots of changes now- other than adding hides- he just wants to feel safe where he is & it's your job to help him do that. Snakes learn their way around, & to survive in the wild, they need to know where to hide for safety from predators & bad weather. How would YOU feel if one day you woke up in a completely alien environment with no explanation? And there was this creature that kept staring at you, & it's at least 100 times bigger than you...?