How many ounces should a 3 weeks newborn be eating a day?

Hi!! Well my son is almost a month!! Wow It goes bu so fast!! Anyway I don't wanna over feed him and make him fat or no I want to not feed him enough!! So how much should I be feeding him...right now I'm feeding him about 4 ounces every 3 hours...my husbnad said not to fee him at night nut I'm not sure of that first time mommie thank you and god bless