Exclusively pumping

Asia
For those of you who pump and feed your little one, how much do they normally eat ? My baby boy is a month old and he eats a min of 3 oz every 2-2.5 hrs sometimes more. 
I find my self pumping and feeding more often than not, so I'm not sure if he's going thru a growth spurt, if he's not getting enough, or just greedy.