Long Lasting Stuck Shed On Head and Upper Neck

[Bogertophis]

Yes, photos would help...? But if he was my snake, I'd use a container that's big enough for him plus either some well-saturated moss or a small soaked
& lightly wrung-out towel (warm water please) & contain him for a while to maximize humidity...you can keep this container IN his normal enclosure, you
don't want him to get chilled...then check back in about 30 minutes & using a damp cloth, gently dampen & then gently rub off the old shed on the top of
his head. Be sure his tail tip has shed completely too, you don't want the old skin restricting the blood circulation there, it can cause tissue death & loss of
the tail tip if that happens.

You mention he is underweight, and it sounds like he is very willing to eat. His bad shed was probably related to 2 things: humidity too low, & malnutrition.
It's possible that there's more at work here than just not eating enough: I recommend getting a fresh stool sample to your vet to check for internal parasites.
If he is sharing his meals with intestinal worms, that would cause all the issues you are seeing...poor sheds and underweight, since they steal nutrients that
he needs to grow & shed properly. Again though, I'm not seeing him...& keep in mind that young snakes do take a long time before we see noticeable growth,
so do be patient. You did say that he was thin upon arrival...bear in mind that some sellers under-feed their animals, but there's no way to know without a
stool check if there is more to it than just not enough food...after all, you've had him for about 2 months already, so if he's been eating regularly he should
be in better condition by now -even if he arrived thin...IMO.

Sounds like you need to cover more of the screen top also...about 90-95%...to keep humidity in. Misting isn't the best way to do this. You might want to
keep a "humid hide box" (filled with very damp moss) in his cage (on warm side), especially when he's going into a shed cycle, from now on. It should help.