Suggest Diet Plan To Be Followed To Cure Difficulty Passing Stools

Hi, My name is Deepthi. My son who is of 3 yrs age feels difficult to pass the stool. We have tried all the medicines to clear the problem. Right now we are using Naturolax(one Tbsp in the evening mixed in 250 ml of water) and Y lax(bed time) to make him pass stool. We give him fruits,leafy vegetables regularly. But still the problem is there. If we use Y lax then only he will pass stool next day other wise he will not pass the stool. What can we do to make him pass stool regularly?Please suggest. Age : 3.8 yrs Height : 120 CMs Weight : 25 Kg How many Liters of water can he take per day? Please advice. As of now he drinks one Liter water per day. Also He doesnt show interest in chewing the food.