
Did you have her checked for retained birthing material immediately after finishing whelping? This could be because she's not feeling well, and if it is going on, she'll be feeling increasingly unwell too. She should be on a high protein diet now, probably not bulk yet although as it gets towards the time you'll be weaning the puppies, at a time they will be making the highest demand on her, she will need all the food you can provide.
She doesn't need MILK!! And especially not cows milk, or Whelpi for that matter. And the suggestion of getting her out of the box with the puppies when you feed her, is a good one.
Do have your vet check her, just in case.