My son has non (?) celiac gluten sensitivity. The main symptom before diagnosis was explosive, horrible, horrible diarrhea. Well this is not a crowd that probably needs me to explain =). But he also has this other extreme. His most recent doctor recommended a book "The Ins and Outs of Poop". Great book with gross name and even grosser pictures. The book makes the case that kids get desensitzed, and stretched out in the colon from having stool held routinely and need a long time to get back on track.
The most popular way is Miralax but I just cannot find the right dose. For one thing, he'll sometimes not drink it all and I have to guess how much he got. If I tell him to drink it, well that's not happening. But when we get him in a groove (by giving really sugary soda to get the miralax down...) he'll get such loose stools that he doesn't make it to the toilet in the morning, not formed at all. If I reduce by one teaspoon, constipated, leaking, very bad behavior.
I have found that suppositories work miracles but my son doesn't agree and I feel like that's something you shouldn't force. I ordered some pedialax chewables from Amazon. Yes, I'm trying to up fiber and fluids (I even sprinkle flax meal on all his starchy foods to hedge them). I know I can do better but I also want my little boy to go to school which is really hard when he is either having diarrhea or constipation.