I agree with most of what has been said. At night time - I don't wake my LO - He will wake when he is hungry. However, during the day, I feed about every 3 hours, which means, on an occasion - yes, I wake my baby up. He only has one long stretch of sleep a day and I want that to be at night.
My LO will be 12 weeks (6 weeks adj.) on Sunday and I feed about 3.5 ounces of formula a feeding and I usually do about 4 ounces before going to bed.
As far as how much you should feed your little one - I have heard about 2.5 ounces per pound. So if your LO is 10 pounds .... then about 25 ounces a day.
As long as he is gaining weight - I wouldn't sweat it. Mommy knows best! :)