Ittybitty just officially turned 3 years old and is not potty trained.

He wears pull ups and has potty-ed (one and two) in the child size potty. He generally doesn't go unless we tell him to sit down on the potty and try. He will sit and go every time instructed.

He had one good day that he went multiple times on his own (to the point that the only reason we knew was because he came out pulling/straightening up his pants). We celebrated, danced, clapped - the whole nine yards. He was proud.

Now he doesn't go on his own at all, only when instructed. And he NEVER does number two in the potty - only in his diaper.

We've tried reminding him to use the potty next time he needs to do number two, he says ok. We've tried letting him sit with his diaper for a little (not long enough to cause any damage) - he could care less. If he is told he stinks (big sis), he gets defensive. And generally, he is just quite content with a messy diaper.

We've asked him flat out how come he doesn't use the potty for when he poops, and he says very nonchalantly "because I don't want to." He's pretty smart, so I know he meant what he said.

Any tips?