Does it look a little like this? This is my Prissy who turned 3 weeks old today and I've been fighting this issue for the past week. Her vent protrudes and poop gets stuck in it. She also chirps when she poops, like it's uncomfortable or hurting. I'm not sure if you're having the same issue but for Prissy, I've concluded that she's at the bottom of the pecking order and not drinking enough water; if any at all. The things I've tried that didn't work are: epsom salt bath, honey water with ACV, electrolyte water, yogurt, water with coconut oil, Prep. H, and feeder mash. What I have done that did seem to work is hydration by dropper every hour or so of either regular water, probiotic water, and molasses water (laxative) because in Prissy's case I think she is constipated due to dehydration. I also continue to put Prep. H on the vent and alternate with coconut oil in hopes that it will start to help shrink her vent. I also clean her vent often and have kept her on the wet feeder mash to promote water intake. As I said, this started a week ago. As of today, her vent doesn't protrude as bad (but it's still a bit of an issue) because the frequent hydration has helped her to feel better (more energetic and more active with less sleeping) and made her poop softer. Another issue I'm having now is that her vent is still quite large due to all the straining and protruding that she has gone through in the past week. It's definitely larger than a normal vent when it's not protruding.
Good luck and I hope your little one gets on the mend soon!