It is very likely that he is reluctant to move his bowels because he anticipates it wuill be uncomfortable/painful. This results from recurrent constipation. Confer with his pediatrician, who may recommend a regimen of laxative and stool softener. Also, be sure to have him sit on the potty on a schedule.
Hi....it may be more than him not liking to go, he may have pain when he goes...do get him to a dr that will do testing for fishers, and other issues...but do talk to ur DS, ask him y he does not like it...ask if he gets pain....and where the pain is.
Good luck
"selma"