When you say he eats well what does he eat plenty of bulk and roughage will help as he does sound constipated ,how about a good bowl of cereal in the morning ,maybe a banana Yoghort..hopefully get green veggies down him but okay kids dont always like them , so peas, beans whole wheat bread ,.Many children dont wipe well and it can be annoying, if you find yourself getting on his case back off a bit as it can make it worse many children hold it in ' from anxiety , let him be in control of his body , less words about it .Good luck
You are not alone. I have a child that is 7 going to be 8 with the same problems. I cut juices by 3 pm and water by 6 pm bed time is 830pm otherwise he will pee the bed. Als0 the doctor recommended more fiber in his diet (to make smaller poops). I also let him use the tablet for up to 15 minutes on the toilet as a reward first thing in the morning and right before bed. Seems he is more relaxed so he has less accidents than if I don't do it at all. he says the poop hurts so that's why he refusing to go. We will see what happens. Also make him/her clean there underwear. Make them responsible and I also started a reward chart. Seeing if that changes at all