Sometimes children will hold back on pooing because they have been constipated in the past and has caused them pain to open their bowels. They are scared that the same thing will happen if they try and go.
Encourage him to sit on the toilet and take his time. Some psychologists reckon a reward system, even if it is only a star chart, will improve things. I would take him to the G.P. as he can be prescribed medication that will make his stools soft and easier to pass.
Poor little mite, I bet he feels awful when he has an accident.
Aaaaw, didn't' realise that...as an adult suffering impacted faeces I'm the opposite, I'm so determined to shift the mass in me as its so horribly painful.... That does stand to reason now for a child..
I would still have a word with the endo as being constipated for me does severely affect my levels.. To go high. (Obviously I'm a mature adult though) they weighed one of my poo after being admitted to hospital it weighed 6lb!!
I would just talk to endo and dietitian because it could be something food wise that causes constipation in the first place. For me I found it easier to write down each day what foods I ate and of I had a poo etc.. Was it normal, or impacted etc and the food that I had ate.
For example Thursday morn I asked hubby to hold his nose and look at my poo as it had solid food in it still. We established that it was food from Sunday last week, so I now know to avoid that food.
It may be worth doing something similar to this for a couple weeks and see if a particular food may be causing any constipation....