I have a young chicken that looks I'll. I haven't had much experience with sick chicken until recently, I've had 2 come down with something. One passed away today as he was very thin, droppings were watery and yellow and lethargic. I put him in another coop away from the rest when I realized he was sick. The remaining chicken is not thin and droppings are not watery but very lethargic and balance is off. I can't find anything on line that describes these symptoms. What can I do?