Oh. gosh, poor baby. Many GSDs have such sensitive skin. Those to me look like infected bites of some sort.
Chigger bites, maybe?
What worked for us on Hans's multiple and constant skin sores was the iodine regimen, plus putting Penaten cream on the sores. Penaten is like a miracle. Zinc accelerates healing and has been a Godsend to us.
The iodine regimen:
A Simple Remedy to Treat Dog Skin Infection
Amazon.com: Penaten Cream ( 150 ml )(Packing Maybe Vary): Health & Personal Care
Penaten goes a very long way. All you need is a very tiny bit, otherwise it gets really sticky.