Is my German Shephard sick or not?

You don't say what you feed your dog. Being 1 yr old, he/she still has a lot of puppy inside and it will try to eat a lot of things during experimentation. It could have eaten something disagreeable at the dog park. Watch to see if it tries to eat lawn gr when outside. Dogs, like people, get upset stomachs and that is one way they alleviate the problem. If the dog continues to have dry heaves, take it back to your vet as soon as possible.