Crate him after exercise. Some dogs get adrenalized by certain activities and have a difficult time turning off afterwards. The more you try to wear them down the more amped up and frantic they become, creating a vicious cycle where they become harder and harder to wear out. Crating can help teach a puppy to settle down and sleep. Puzzle toys can also help mentally exercise a puppy. You don't have to run out and buy a bunch of expensive toys. Put a meal in a paper bag, scrunch the top and let him work out how to get the food out, place a meal in a muffin tin, put some kibble in a low container and put some plastic bottles in for the puppy to push around, put kibble into a plastic bottle without a top and let him bash it around, ect...
Be careful about forcing your puppy to exercise. Joints are not fully developed and damage done now will be have life long affects. Puppies need exercise, but too much is not good. My personal choice is low impact at the puppy's pace on a natural surface. I avoid hard surfaces and rarely walk a puppy on a leash. I don't do forced exercise like running, jogging, on leash walks, or a lot fetch. I use fetch for training, but not exercise.
GSD puppies bite. I know some people get very upset by it, but I'm not really bothered by it. They are a herding breed, they bite a lot, but it is a phase that will pass with teething in most cases. Its part of owning a GSD puppy, they are intense and they are bred to bite things. To me biting means my puppy wants to interact with me, it just doesn't know how yet, so I redirect and channel the need to chase and bite into more appropriate activities. I like a pushy puppy, so I'll take biting over a puppy that would rather play by itself.
If all you have is a hammer, everything looks like a nail.