Has anyone had a newborn they constantly had to wake for feedings?

My 5 day old baby very rarely wakes on her own for feedings. We were letting her determine her own feeding schedule while we were in the hospital but once we got home, she rarely woke on her own and started losing weight. Obviously we couldn't keep doing this, so we wake her every two hours during the day, and three at night to feed 1-2 oz's each time. She's also very difficult to wake for feedings, but was seen by the dr today who wasn't concerned about that. Said some babies can sleep up to 22 hours a day. I'm just frustrated that she doesn't seem to wake at all when she's hungry, and when we do wake her, we have to make an effort to keep her awake for the rest of the feeding. Just a frustrated new mom needing advice. :-\