I bought 3 Rhode Island reds (about 18 weeks old) last Thursday from a local farm. They are my first chickens, so I'm new to this. One seemed listless last evening, and this morning she has one eye shut and is staying off to herself, not eating or drinking. Doesn't seem to have any discharge from nose. I'm going to isolate her in a cage we have, and I read about putting apple cider vinegar into her water and giving yogurt. Also will try a cooked egg yolk. What else should I do? Should I get an antibiotic? Advice would REALLY be appreciated.