This is very normal of GSD pups and all pups honestly. They are born with their ears down, they do a bunch of tricks similar to what you'd see a gymnist doing, then usually they stand for a while and when puppy starts to teeth they can start doing tricks or completely drop again. A small amount of vitamin C and E during this time can help with that but please speak with your vet before any supplementing. You aren't alone! A friend's Pharaoh Hound puppy did not get his ears until he was EIGHT months old. They were worried! Though he got a reserve once and the photo is quite funny (in retrospect!).
Good luck with your pup!