My 4 year old refuses to use the bathroom

My son has been potty trained for over a year now. Recently he stopped having a bowel movement in the potty. He will hold it in, and stop it until it comes out in little balls. We have tried encouraging him to use the potty it does not help. Discipline does not help either. We have tried having him walk around naked so he can't hide the fact that he is stopping himself, he still tries to stop it. We tried putting him up there for 5 minutes every hour and nothing. Now he is holding in his pee too. I am afraid he is going to make himself sick. We recently had a new baby (7 weeks ago) but he does not have a problem with her. He talks about her all the time and helps a lot. He gets just as much attention as she does. What can I do to help him start using the potty again?

[Kele2432]

Are you sure he isn't constipated.  If he is pooping in "nuggets" or little balls... that is probably the case.  I had the same problem when I was younger.  My mom used to give me castor oil.  That seemed to solve the problem. best of luck!