7 yr old son history of fecal impaction has super hard knot under belly button. constipated. occasional cramping. started miralax. what else to do?

Time for work: Kids don't get to that state overnight and will not get over it quickly.You need to find a Developmental pediatrician or pediatric GI specialist to come up with a bowel rehabilitation program. This can take up to a year & involves scheduled emptying, oral softeners like miralax taken for months at a time & followup visits.You can get a normal kid back but it will take work.