Chicken Coughing and Sneezing

[Super Chickenman]

I have a gold sex link that is coughing and sneezing. She started this about 3 weeks ago when we brought them home. Thinking they might all get sick, I gave them Agrimycin-343 in their water. She ceased the behavior almost immediately. Last night... it came back. I have again redosed with the agrimycin. I have not found any poop that looks out of the ordinary. (they are free ranging though). I am using pine shavings for bedding and pine shavings and oat or barley straw for nest boxes. Is she alergic to something? Is there something else I should be giving her? Is this a normal thing even?

 

[Super Chickenman]

Can anyone help with this? I went out and watched her tonight. She seems healthy, bright, alert. Eyes are clear and no snottyness.