I am new to raising chickens and have a question about the health of one of my silkie hens. It seems that she is coughing or sneezing more and more lately. I have added a vitamine booster and antibiotic to their water. I am not noticing any improvement after 2 weeks. Only one of my hens seems to be behaving this way. Any suggestions as to what I might be doing wrong and what I can be doing better?