one of my black sex links is having probs. looks like she's yawning, stretching her neck out and trying to swallow air. i dont know what it could be. she's a bit large in the abdomen, but i thought maybe she was just larger than the other hens. i dont know what to do. i'm quite worried. no other chickens are doing this and she may have had symptoms since last week where i cought her doing almost the same thing, i just thought maybe it was a full crop. can someone please help?