Hen is approximately six months old, today is exactly 3 weeks in quarantine. Yesterday she was eating, drinking, scratching in the dirt and looked fine but maybe a little quiet. By midday today she seemed droopy and put herself in the coop way before bedtime, and started sneezing. Loudly, strongly but just occasionally at first. But then more frequently. Honestly I was worried the noise would attract predators so at dusk I caught her and put her in an isolation cage to observe. The sneezing is loud enough it probably hurts, and it got more frequent. No discharge, no foamy eyes, no swelling. Holds mouth open to take a breath, and her breathing is audible/like a moan or growl. She is well enough to stand. Passing some yellowish liquid, with tiny bits of green so she did not eat much today. I figured I'd best get her started on something, because the sneezing is so strong and progressive. Gave her Tylan, and she's warm and safe, with some water laced with sugar and vitamins; some food moistened with yogurt. I've studied all the symptom charts, and ratting/sneezing does not narrow things down. There was another hen from the new group that showed rattling and open mouthed breathing (but not the incessant sneezing) on day 3 of quarantine. I gave her away to an experienced chicken person who wanted to treat her. She was on duramycin and has recovered. Yet another just acted cold/puffy/droopy and did not eat or drink for a few days-- 3 days of Tylan fixed her up, but I did the full 5 days. She remains well. We've just finished a couple of days of cold, rainy, windy weather. I know chickens don't get "colds" but might be a contributing factor. Any ideas what I'm dealing with here?