Help! Duck

[felicity5]

My pekin duck (7 months old) has become anti social and distant. He is usually slightly aggressive and chases and always eats food but now he isn't eating (not even his favourite worms!) he doesn't follow his other duck friend and walks as far away from humans and hides.
He is waddling funny and I went to pick him up and he couldn't run he was stumbling and falling forward. I don't know what's wrong with him!! Please help