One of my chickens is sneezing! She has been sneezing for a while now, maybe a week or more. She and her sisters are 8 weeks old. Others seem to be sneezing a little, although not as much as this girl. There are no other symptoms, but sometimes she shakes her head, or stands and looks off into the distance, like she's in a trance for a few seconds, which is probably normal. Please help! I'm worried about them!