Unfortunately I think you might be right. Whole grains for a chick that small may well have caused an impaction somewhere. I would cut the scratch out altogether. If you want to treat your chickens, a few meal worms is a much healthier option. They would all be better off on chick starter, if you want to simplify everything and just give the layers access to oyster shell on the side. You could also ferment the chick starter or just make a mash with it, which will help improve digestion and ensure they are getting more fluids with their feed.
I now realise what the photo is showing....I couldn't make it out before (eyesight is failing), but now I see it..... your chick has a prolapse!!...I was thinking that was a fuzzy photo of it's head and beak ....Eek! Don't know why I didn't pick up on that, especially when you mentioned haemorrhoid cream! I must be going senile as well!
I don't think I can suggest anything else on top of what you are doing other than to keep that vent moist and lubricated and perhaps try to very gently push it back in.
Good luck with it and keep us posted on it's progress.
Regards
Barbara