I agree with the other post - work out a way to get OFF of Miralax. Two things which can be read on the package insert from the drug company - 1. Miralax should not be used for more than TWO weeks and secondly, it was NEVER tested on children prior to being prescribed to children. However, parents are never told this information.
He needs a whole gut-bowel check up it seems. Has he been on frequent antibiotics? Do he drink enough water? Has he been tested for intolerances to dairy or gluten?
Here's what I would eliminate:
1. Dairy is VERY constipating. Remove all of it for one month (and his bones won't crack, fall apart). This means, yogurt, milk, butter, goldfish crackers and the like.
2. Add a good probiotic to his diet. Check at Whole Foods or Fruitful Yield.
3. Natural calm is a natural fizzy drink (again Whole Food or Fruitful Yield) that can be used to loosen his stools. It's non habit forming and magnesium which many of us are deficient in.
4. Add lots of fresh fruits and veggies to his diet. Raspberries are HIGH in fiber as well as pears, apples, blueberries, etc. Leave the skin on.
Our family takes a whole food supplement called Juice PLUS+ and it has helped also with bowel movements (powdered produce of fruits and veggies) for two younger children. Let me know if you have questions about this product.