This may help. Give your son 1 tbsp of flax oil every morning. It is almost tasteless and has no oily film after affects in the mouth. This will make his BMs so smooth and easy he will have no problem with hurts etc. This way you can at least rule out the "hurt" aspect of it. If this doesn't work then I guess he really does have a problem. At eight years old these things should all be behind him. Hope this helps you and yours.