Certainly you should check for mastitis etc as the other have suggested, however I had a young bitch like this - she did not want the babies to "cramp her style" and she would sit out and just watch them for hours.
She was confined in the same area as her whelping box and could come and go as she wished, and the pups showed no adverse effects from this treatment. She did sleep with them at night although I have no way of knowing if she spent all the night with them.
Dr J.E. Mosier DVM in Pediatric Care (an article written for Uncle Bens Australia in 1982 - yes I know it is a long time ago!) talking about feeding orphan pups says " The number of feedings per day may vary from 3 to 12. . . . . The greater the number of feedings the greater the liklihood that the puppy can be maintained on comparable condition to a well fed nursing puppy"
So he is saying that you can feed orphan pups as infrequently as every eight hours and I have certainly found this to be true although probably not desireable.