Great suggestions here especaily from DJsmom. I would add that what you describe sounds a lot like me, I am hanging in there pumping just keeping ahead of the game. (ds was 12 lbs at 4 week checkup after 81/2 at birth) Just adding too that my ds hit growth spurts at 6 wks and just now at 3 months. I read about it here and realized it was pretty normal that he was acting razy hungry and like he wasn't getting enough, I just fed him as much as I could and things evened out in about 4 days.
Keep reading around here too, I am sure you will find lots of good advice and encouragement.