K.G.
Is he not going on the toilet because you think he's constipated or because he just doesn't want to??
In my situtation, I had a 3 year old boy who was peeing on the toilet no problem, but pooped in his pants everytime he could! After a while I just couldn't take it anymore and nothing I did worked. So, I took him to WalMart and I let him pick out any toy he wanted...He picked out a bike. When we got home my husband assembled it while my son was watching and getting very excited to play with it. We put it up on the kitchen table and said he couldn't play with it until he pooped on the potty. The very next time he had to go, he went on the potty and got to play with his toy. The next time he had to go he pooped in his pants again so we took it away. When he went on the potty again he got it back. NOw, he poops on the potty everytime...never a problem again. I'm not big on using bribes to get my kid to do something, but sometimes it just works.