Has he been trying to move around at all? Like to get up or walk or anything like that? I would definitely give him electrolytes (or honey or molasses) in his water, there is something called Nutri-Drench that I’m currently giving to my failure to thrive chick..you can add it to his water or even put a few drops directly into his mouth.
Topical preparation H for the vent or other hemorroidal cream, and push it back in.
My daughter was 15 months old when we drove to Florida and while we obviously stopped a lot, her sitting for long periods sort of impacted her stool and she became constipated. Not fun trying to explain putting KY (all they sold at the gas station) on a screaming toddlers bum, in a gas station restroom in the middle of the night lol
On another note..if he is trying to move around, possibly a visit to his flock would be uplifting for him? He’s also scared and not knowing what’s happening to him so perhaps some normality would help