Breastfeeding

Ok. So when my son was first born, he would eat for 20-30 mins at a time... ON ONE BOOB!!! now I'm lucky if he eats like 5-8 mins on one boob. But then he will be content for a couple hours. Sometimes he will want to eat every hour, but if I try keep him on longer he just plays with my nipple and ends up spitting up. Does anyone else's baby do that? Eats for such a little time...