Hi there
A baby is much more efficient at getting milk out of your breasts than a pump. So, even though you got 4.5 ounces, baby could probably be getting more out, and it should be enough to sustain him if he has enough wet and poopy nappies every day.
6 - 8 wet nappies a day, breastfed babies can have a poop every day or one every 7 days. It varies, so unless baby is constipated (very rare with bf babies), I don't think you should worry about poop nappies. Just check for the wet nappies.
I hope this helps.