Hey, i bought my Hens around 8 weeks ago, and now one seems quite poorly.

They are about 12-15 weeks now i think, not too sure, not laying.
One seems perfectly fine, pecks about everywhere, very perky. The other however, seems very lethargic, head always hunched in as if shes always asleep, she does have a wonder round, a drink everyso often, and a peck at her food now and again, but she is alot smaller than the other one, and seems light-ish. Yelloey/orangey poop... and she seems to labour her breathing a little, i massage her neck and chest every so often, and that seems to make her open her neck and beak more....but still seems forced breathing.

Any ideas or suggestions??