Hey guys, I have a 7 month old hen that started breathing heavy and will not walk much for 2 days now. I have her inside and administered Vet RX to her. I have electrolytes in her water and fresh food. She is still eating and drinking. She has no runny nose or wheezing. What can this be?? I've checked for mites as well. All my other chickens are fine. Thanks in advance to any help!