6.5 year old is pooping his pants - please help me!

We've got a 6.5 year old son - extremely bright and no delays noted whatsoever - except for shitting his pants. He potty trained normally at about three, and then at about 4.5 we went on vacation and he had a particularl nasty bout of constipation (because he was afraid of the toilet at the hotel) and from henceforth decided that pooping was not for him. We have checked all the boxes for chronic constipation - miralax, dietary changes, etc - and I really don't think it's an issue with him being able to go. He CAN go - in fact when/IF we manage to get him in a reliable routine where he's going often we can go a few months without there being an issue. Granted, we have to keep reminders on our phones to remind him to go - but he can do it. The problem, I'm convinced, is psychological. Anytime we go on vacation or school starts or really anything that's too interesting for him to stop what he's doing and poop - we regress. When we regress, pooping becomes this huge issue. We'll make him sit and try to go and he'll sit there for hours - through homework, lessons, dinner, bedtime - crying and carrying on because he's missing out. Whining that he can't go, etc.I'm really at a loss at this point. We're in the third year of dealing with this, we have one, going on two, other children in diapers and I CANNOT be wiping shit out of my seven year old's underwear along with the other two kids. I do make him help me, but helping with the cleaning seems to cause more mess than I'm already dealing with more often than not so we share the task (fun fact, cleaning shit out of a tiny pair of underpants is not easy!)It's about to get to the point where he's being teased at school. This morning, two seconds before the bus came I smelled poop on him. Sure enough there's a turd in his pants, like not just a skid mark, but an honest to god turd like he's used his pants as a diaper. And he was going to go off to school like that! He left for school crying because he was embarrassed to have me clean him up. Well, if you're embarrassed, WHY ARE YOU DOING THIS?What do I do? Do we need to bring in a psychologist or something at this point? I don't even know what the hell they'd talk about except for the fact that he doesn't want to go to the damned bathroom. It can't be normal for a child this age to be ok with having poop all over his body. Please help, I'm so frustrated!EDIT: We've brought it to the pediatrician and they suggested miralax and dietary changes for constipation. It made it 10x worse because he's not constipated as far as I can tell - so loosening his bowels just gave him uncontrollable diarrhea. via /r/Parenting https://ift.tt/2NRGdAu