I have tought my GSD many tricks , he is only 15 weeks old and is trying to learn stand and give 10. the problem is dat he can't balance on his hind legs. if i lift up his 2 front paws he looks wobbly and can't keep them up by himself

this is normal right? I guess he is still growing and he is so chubby and out of proportion he can't keep balance? my worst fear is that he has weak hips or hip dysplasia but he is very active , never sluggish and loves to run. ne1 have this problem with bigger breeds , i have a poodle to and he always likes to stand up on his hind legs.

Don't attempt to teach this until he's at least 12 months old.

You beat me to it JG ....

Dogs have four legs for a reason - we wouldn't hop about on one for example if given the choice.   Pups should be allowed to grow and develop naturally without any excess strains - encouraging him onto his back legs is highly ill advised.  Teri ;)

Also how much is your GSD running, you really need to restrict this in a big dog?