I am new to having chickens. I got two about 3 months ago and then 1 more a week later. Those 3 three have been fine. They are probably less than 6 months old. Last week I got two more. I have been keeping the two separated from the others. The next day, I noticed one of the two kept closing her eyes and keeping them shut while eating or drinking. Then I noticed it making a coughing or hacking sound every minute or so. She also seems not as active as the other chick. Again, I have been keeping the two new chickens separate from the other 3, but tonight I noticed one of the first 3 acting lethargic and heard a cough coming from her. From what I've read I see this may be a respiratory illness? What medicine or treatment should I use? Should I isolate the new chick with the cough and the older chick that I just noticed a cough? I know this explanation may be hard to follow, but I am very new to having chickens and could use ANY advice. Thank you!