please help

OK, first of all how much exercise does your dog get and how much mental stimulation? (games, training?)

2, what training has he had?  Does he know "sit" or "lie down"?

3. Is he on "NILIF"? 

4, what have you done so far to combat this problem?

5,WHEN does he do this?  Is it when he is at home with you?  Is it when you come in the house after being away? Is it when he gets ramped up when playing?

As you say, he is a puppy and he is playing.  He doesn't know taht this hurts you and is not an "OK" way to play.  What you need to do is teach him an alternative way to play that is still fun for him, but doesn't involve jumping up and nipping.  At the same time, you need to STOP all games, fun and attention the moment he jumps/nips.  You need to be SUPER CONSISTANT about this. 

Do not raise your voice, tell him off, tell him "NO", don't even LOOK at him.  He is doing it for ATTENTION.  You literally need to FREEZE and stare into the distance.  If you push him away he is likely to take this as you joining in the game and he will come back for more.  This is very similar to how dogs play together, so by pushing at him you will confuse him.  On the other hand, if a puppy gets too rough with anotehr dog, that dog will freeze andturn their head away.  Watch them closely next time you get chance and you will see.  THAT is the behaviour you want to copy.

If he persits you could either (a) gently hold his collar while still freezing and staring away or (b) leave the room (calmly) for one minute.  If he does it again remember you you need to repeat IMMEDIATELY.  It IS frustrating, but he must NOT sense your frustration/anger.  Don't let him "push your buttons"!  Stay calm. 

I think your dog should also be on "Learn to earn" (NILIF) if he isnt already. 

There are a lot of tips in this thread about this topic.

Everything Chuffy said!

Everything Chuffy said was good.

I would ask how old was the puppy when you got him and how long have you had him? Point being that he may have not learned how to play properly, at least with humans. One thing you can do when he nips is yelp, like a puppy that's hurt, even if it's not really hurting you right now. When he gets to be a bout a year and a half old, he will have some serious muscle and grown up teeth. That is how dogs learn bite inhibition in the litter. He can't know it's too hard unless you or another puppy let's him know. As well as rewarding for not nipping. Also, negative punishment. When he does the nipping or mouthing, peel your hand inward and away from his mouth and turn away. When he calms down, turn back around and give affection. I used that with my dog, plus reward training for not jumping and mouthing. Also, I put jump on cue. If I don't ask for it, he is less likely to do it as it is only the best reward if I ask for it. I have a general command "off" which means to disengage from whatever. It is generalized because I have used it in various circumstances.

 I think I would not do the yelping thing at this point.  He's ten months old and knows pretty well what his jaws are capable of, regardless of how he was raised.  Plus, his mental makeup has shifted from when he was a little puppy, when the desire to please others was strongest.  Now that desire is probably at its low point in his whole life, being overwhelmed by teenaged enthusiasm and newly-awakened instincts.  One of those is prey drive and yelping would probably be reinforcing rather than aversive!  Yay!  Squeeky toy!!  Remember in Ring training (not sure about Sch) the targets in the padded suits yell and kick up a fuss and it's supposed to increase their drive.

Here's where you can find the material on "Nothing in Life Is Free." http://www.ddfl.org/tips_dogs.htm  I also strongly encourage you to find ways to involve your German Shepherd in your life more - these dogs really like routine and structured training, so if you haven't already, start formal classes with your dog and drill the exercises you learn a couple times a day, preferably at the same time each day.  Teach the dog to work for some play reward, like a tough tug toy like a big rope toy or one of those canvas on a rope dummies (this will also teach the dog an appropriate outlet for the biting). 

The good news is that your dog wants your attention very much - it's up to you to allow him to be the terrific partner he wants to be, in your life!