My Son Is 7 Years Old And Was Once Fully

My son is 7 years old and was once fully potty trained but now is no longer using bathroom to poop he says he can't help it but tells us to clean him he has seen several doctors and specialist test show nothing wrong he has seen therapist but nothing helps we have even had him tested for autism and any special needs and everyone says he's fine nothing wrong punishing him does not work him getting made fun of at school doesn't push him to use bathroom I'm frustrated why won't he potty train diapers r expensive