is from the diapering the babies, you can try a bit of extra virgin coconut oil, my chanel loves it, and as soon as she whelped i gave her a 1/4 of a teaspoon, not her normal dose but it helped inmensly, I asked my holistic vet and she said it was ok, for her to have it, also it helped keeping her coat nice while she was lactating. We do the coconut oil therapy with all our dogs.
hugs,
Carmen in nj