As the title says, I've raised a Pekin duck and it's been 3 months since it was a duckling. But now that it's grown a lot, it's larger and heavier. I noticed now that it's having a hard time walking, very wobbley and unstable. I always to him to the backyard to the kiddy pool, and while having him walk half way there, he just gives out and lays there. This worries me, whenever I try to carry him, he refuses, and keeps walking even if he's obviously suffering from not being able to walk right. What should I do?