Baby not eating enough

Mommy

My almost 3 week old will eat about 3 oz in a 4 hour period, then maybe 3 more in another 4 hour period. But that's pretty much it all day. Is 6 oz a day normal? He's pooping and peeing just fine. I don't have him on a feeding schedule whenever he starts to get fussy I feed him. Should I not feed him for a couple hours so he can get hungry? And then take a bottle at one time, not over a 4 hour span?