Stomach pain everyday before stool.

Hi My 2.8 yr old son is complaining of stomach pain everyday which comes for 15-20 sec and then he goes for motion. He passes motion for 3-5 times a day.Before motion he says, he is having pain in stomach. The motion is not normal, sometimes it is loose , some times it is semi solid, sometimes I see the food in his stool like carrots, onions ,apple..  I feel like he is not chewing the food properly, and I ask him to chew well. Since last 15 days he is complaining of this vanishing pain. Given enterogermina for 5 days. Still the issue persists. He eats fruits, rice , veg, dal, drinks water, milk , 4-5 biscuits a day , peanut chikki, flattened rice chikki etc. For the past 15 days. Sometimes he wakes up for motion mid of the night/ early in the morning complaining pain. He plays very well, his physical activity is good. He puts hands in his mouth while playing or watching tv. Dont know what could be the reason for his pain.. please suggest.