need help

Loeffelholz

my 3 year old refuses to go poop he is not constipated he just wont go i need serious help ive talked to the doctor and am doing everything theyve told us sitting him on there for an hour rewards everything and he wont go he is on a high fiber diet and takes miralax every night along with a supository only when he is crying it hurts his belly so bad i feel so bad for him what do i do