I would immediately change your feeding schedule. Feed in separate rooms through whelping and until the litter has been sold. GSDs are known for moderate same sex aggression…throwing pregnancy into that mix increases that instinct.
Your breed mentor should have told you this.
As fast as it appeared my guesses are insect bite or injury. Although it is impossible to diagnose any skin lesion without examining it. I would recommend watching it for changes and if it is not looking better by Friday have your vet look at it.
Good Luck
Thank you. It is almost gone this morning, so I guess it was just a bite or scratch of some sort. I’m still watching it and will bring him in if it changes again.