I Have A 5yo Child Who Has Had Pain Of

I have a 5yo child who has had pain of his bottom at times to the point he will roll around on the floor crying complaining of pain. This usually occurs when trying to pass stool. He has hard pellet like stools, will not use the bathroom at school due to him having to have me or his mom wipe him. My ex-wife claims that I am not cleaning his rectum causing this pain but we bathe him every day when he stays with me which is often no more than 2-3days at a time. No blood has been noted. He is a picky eater. What should I look for or do for him. Thank you.