He pees outside but he will NOT poop. He is about 16 weeks old, and we have had him for about 2 months. He started doing really well, but now he has regressed. If we catch him squatting and take him out he won't go, and we have him outside for 10+ minutes. He waits for the split second that we can't see him and he does his business on the carpet! What do I do??