It seems that your child has some underlying chronic problems.
Please check the following general steps -
1. Let your child drink a lot of fluid / water. Dehydration
can cause constipation
in many cases.
2. Maintain a good bowel habit. Let your child a lot of time in toilet if he is not passing stool. Retained stool get dried and hardened. It is more difficult and painful to pass a hard stool. The child try to retain that, which actually cause more constipation. Thus the vicious cycle goes on.
3. Decrease the milk (and milk products) from his diet.
4. Please check the defecation posture. Natural defecation posture is squatting. Get your child habituated to defecating in squatting posture, if he is not already doing it. Posture is an established cause behind primary constipation.
5. Give him fiber rich diet (I know you do), and remove Fiber less foods (like banana, milk and dairy products, refined cereals, white bread etc).
If the constipation still persists after the above general measures, please get your son thoroughly examined by pediatrician
. The causes could be -
1. Hirschsprung's disease - is most commonly associated cause. The improper movement of muscle in intestine is the cause behind it.
- Low thyroid hormone slows down the muscle activity in intestine.
3. Cystic fibrosis
Hence, I would suggest you to visit a pediatrician as I hope the general steps are already done.(If not, please follow these).
Please post if you have more queries.