What Causes Abdominal Discomfort While Passing Stools In Children?

hi my names clarissa (21 years old)I have a four year old son who has trouble with his bowls he refuses to let me give him an enema, his belly is distended and he tries to go to the bathroom but he holds it in by crossing his legs. He is also a very hyper child and gets agitated very quickly, he use to be very happy and easy going, could this be a side affect from not having normal bowels? how can I help him? (he refuses the hospital and doctors as well because of the enemas they have given him in the past he is afraid.