I'm new to raising chickens and have 4 hens. One Rhode Island Red is a little lethargic, has watery poops, and her comb is dark red (all other hens have vibrant red combs). Her rear has been messy for about two weeks and she is starting to lose her feathers back there but her vent is clear. Her appetite seems the good. I found a weird looking mucusy sac in the nesting box he other day and I don't think she has produced an egg for over 2 weeks. Does anyone know what is wrong and what I can do?