C.B.
My daughter was very compacted (colon and large intestine filled with hard stool) and if we gave her some Miralax it seemed like she had diahhrea. The GI specialist we finally saw after 3 months of cramps and hard then loose stool explained the following. Your stomach breaks down the food and adds liquid so all the food in your small intestines is liquid until it gets to the beginning of the large intestine. If your large intestine is full of hard poop, eventually the liquid from the small intestines can seep by and make it seem like you have diahhrea but you are actually still compacted. Our GI doctor put my daughter on a 2 day clean out regimen similar to when you have to undergo a colonoscopy, then on a maintenance dose of Miralax for a month when we saw her again. We saw our pediatrician 3 times in 3 months and she recommended more liquids, some miralax, even put my daughter on 2 weeks of Prilosec all without much improvement. The GI specialist diagnosed her right away and took some x-rays and addressed the real problem. I would see your pediatrician and if the advice seems like it will not help ask for a referral to a Gastro Interologist.
PS: many kids become constipated when they switch from diapers to potty and start withholding going to the potty until their body can no longer really hold it.