It is totally normal for a newborn to be hungry all the time! Some eat more than others. Some eat fast, some eat slow. It is not a good idea to measure or monitor how much an infant eats though. Just let him dictate what he needs and when he needs it. Most babies that age will eat every 2-3 hours! He will stop when he is full. There is no need to put a baby under 6 mos on a schedule or limit their feedings.
And by all means do NOT even think about giving that baby cereal! He is WAY too young. It can damage his intestines and set him up for food allergies for life. Wait until he is at least 6 mos old before introducing cereal. It does not help them sleep longer. Babies sleep through the night when their brains are chemically ready, you can't influence when they do.
Breastfeeding is great because you're not aware of exactly how many ounces the baby is eating, you just know they are getting what they need and they stop when full. It's easy on your brain, no thinking involved! Just bonding time. If you are not getting much sleep, keep the baby in bed with you and nurse in bed, then you don't have to wake up.
If you are doing formula already, make several bottles so you won't be upset when he finishes off one and wants another. You don't need to measure or monitor unless your doctor thinks something is wrong like a baby is not gaining enough weight.
There is also a growth spurt at 3 weeks I think! Relax and I hope you get to enjoy this stage of life instead of stressing!