How do yo make a newborn kitten defecate correctly?

I am caring for a newborn kitten born this past Thursday. He is doing really good and eat just fine. I make sure I burp him after he eats and I make him go potty often. However, I don't think he "poops" enough. His little belly is really fat, like bloated. But he does not seem to be in any pain. When I rub his bottom to make him potty, he does not poop. He poops when I rub his backside close to his bottom and I have to rub it firmly. How can I make this easier for him? When it's time for him to eat, he eats! But like I said, his tummy is really fat. What should I do?