One of my two and a half year old hens has a very pale comb and face. She is sleepy and doesn't move around as much as she use to. when she does she moves slowly. she still eats and will go on the perch with the others. she just doesn't seem to have any energy any more. she has been like this for a couple of days. the rest of the flock is healthy and active. any advice would be appeciated.