There is a good reason GSD puppies have been given the nickname "land sharks". Most are bitey little monsters when they are babies. We have a little 9 week old shark here at the moment and he certainly earns the land shark title.
The best thing you can do is have lots of toys, chews and treats around. When he bites, put something else in his mouth. Redirect and praise, and redirect and praise... They will grow out of it in time. If he gets too wild, put him in his crate and walk away for a few minutes and let him calm down, or take him outside where there more interesting things to do and explore than trying to eat you, lol.
Good luck and remember, it does get better. Trying to 'correct' a puppy so young really doesn't do much good. It can be tough, but stay positive, they do grow out of the mouthing.
Omen v Wolfstraum
Jasmine Katie v Doolanshaus