4 week old eating too much?

When my son was 3 weeks, he went from eating 3oz to 4oz overnight. This concerned me enough. He gained two pounds in two weeks, and so far the doctors have only praised us on his weight gain (he went at two weeks, not since, and doesn't have an igned pediatrician yet). And once again, just about overnight, 4oz isn't enough for him. He roots like crazy, trying to get anything in his mouth. I try to pacifier, but that only works until he realizes that nothing is coming out of it, and then the screaming starts. I gave him 5oz, and he is still acting starved. He is up to 10 lbs 2oz, and was born at 7lbs 12oz.