how many

my nine week old is finishing a whole 4oz formula bottle and still show signs of hunger. i let him nurse until he’s full but then he’ll throw it all up a little while later. i plan to switch back to breast milk since my supply is slowly coming back but for right now i’m just thinking of upping his formula intake. am i feeding him too less? i know all babies are different. how much is your two month old drinking and how often?