I would bathe him with a neutral odor shampoo and then see if the smell returns. Watch him closely so he can't roll into anything smelly. If that same smell returns I would take him to the vet. Young GSD pups shouldn't have a strong dog odor.
Not to scare you but this was the first sign of WD's auto immune disease (I lost him to it) so that's why I am cautious about this.
Deja, GSD, sable WL, female, born 11 / 2013
Cam, Rough Collie, sable, male, born 8/2015