I agree with the other posts that say she may just be saving it up or inherently mellow. You also might want to have her double-checked for jaundice again... one of the symptoms is lethargy (ie: waking them up to eat). Don't hesitate to call your pediatrican if you're concerned though, that's what they are there for!!
My four week old takes a lot longer to get to the "wailing" stage for wet diapers, feedings, etc. than her 2.5 year old sister did! It's kind of nice to hear her starting to rouse herself awake and give me time to get ready to feed or change her. She also slept 5 hours at a time several nights in her first week home, so that was only one middle of the night feeding. Her pediatrician said that as long as she was eating during the day, producing lots of wet diapers (holy moly can this little one pee!), and seemed happy, I didn't need to wake her up to feed her. She said women are told to do that the first few days of life to make sure they nurse as much as possible to help establish milk supply in addition to monitoring the baby.
Congrats to you and your husband!