How much are you giving him at each feeding?
Perhaps its just more and more often than he needs now.
HRH is small, so comparing her might not be apropos, but she eats twice a day. 3/4 to 1 cup each meal depending on if she's getting yogurt or not. The few times we have given her a third meal when we are eating lunch she has only gotten 1/2 cup and doesn't usually eat it all. So we also cut the dinner meal to 1/2 cup.