I'm not really experienced enough to give you any advice but I belong to a breeding group and maybe someone there will have some advice for you too in addition to the advice you've gotten here. There is a also a formula recipe on there that many people swear by! Here's the link:
CanineReproPuppyCare : Canine Repro & Puppy Intensive Care
I wish you luck! I've only had one litter and we lost one little boy so I know just how you feel!