C.T.
Yep! Many kids find pooping on the potty to be scary or intimidating. My son was pee-trained for a few months before he was poop-trained, and he did exactly what you are describing: he held it until I put on his nap/night time diaper, then pooped. What worked for my son was breaking it into steps. I told him that any time he wanted to poop, I would put him in a diaper, BUT he had to be inside the bathroom while pooping. Once he was comfortable with that, I told him he had to sit in the bathroom, and I gave him the choice of a chair, the floor, or the toilet (still in a diaper). He chose the floor. Next step was sitting on the potty, in a diaper, to poop. Once he did that, even just once, he knew he could do it in the toilet, and he was eager to poop on the potty (without a diaper). From that first time, he was fully day-time trained! Good luck!