I have consulted my vet several times as my puppy always love to scratch and these are what I was told to be the source of her itch:
1. Things she eats/drinks/bites/chews (be it daily meals or tibits-rewards),
2. Places she sleeps/plays,
3. Shampoo she uses,
4. Clothes (if any) she wears.
My puppy is on the verge of recovery as we have found item 1,3 to be the source of her itch.
Please share your experience with this forum.