I have a 3wk old duck who kept falling on his back and not being able to get up. I brought him in for 3 days and gave him Niacin. He seemed a little bit better so I put him back outside, he was fine for a few hours and started falling over again. He leans to his left side and puts his left wing down when he tries to walk. I keep going out to check on him and he is usually stuck on his back. I don't know what to do or what else may be wrong with him. Please help!