New here- I have a 7 week old polish who is very ill. We have had her about 3 weeks- the following started 2 days ago: She doesn't want to open her eyes, fluffs feathers, very thin, when she gets up to walk she walks drunk, she is overall very listless and won't really eat on her own. She doesn't have much head control and is very sleepy. When she lays on her side her legs are tucked, toes curled. When she does sit up, she tucks her head and it slowly falls to the floor and she appears to be sleeping. Head is very floppy when I pick her up so I have to be careful to support her head. When she fulls wakes up she does have better head control. I have given her NutriDrench, electrolyte water, and vit b sup. Because nothing was working I decided to give her water soluble abx which seemed to help and she seemed to perk up a bit this afternoon but has now regressed again. This afternoon when she was more with it she did peck at some of her cumbles and try to drink. Still pooping only because I am essentially feeding her with a dropper several times a day.
New symptoms tonight: she was trembling and after I fed her we put her back on heat. Also while I was feeding her she would open her beak and leave it open (gapping?) almost half passed out, or maybe open for more food? Her 3 siblings are fine and she has been quarantined. The 4 were on corid for what I thought was a few days (husband said more like 7) prior to her getting sick.  Coop is in garage, no heat as they are fully feathered. Coops gets cleaned almost daily. We have been putting them into the nesting area at night because they won't go in by themselves. A few nights ago we didn't put them in...maybe she got too cold?
My neighbor who has had chickens for years came down today to assess and the only thing she could come up with was failure to thrive. She said while her feathering looked good she had never seen a bird so thin. Worms? Nothing that I can see in her poop (but that doesn't mean no worms) and she is so sick I don't want to load her up on MORE meds... although I suppose at this point it isn't going to hurt.....
any ideas would be helpful, we are at a loss. I didn't think she would make it through the night last night but she did. Tonight, fingers crossed. I told hubby tonight we needed to research how to euthanize her humanly as she can't go on like this for long, it isn't humane. He was near tears.....
brooder pneumonia? Corid OD? mold? vitamin deficiency? I have spent hours upon hours and cannot seem to find anything that really fits these symptoms. No chicken vets around-
Thank you for any input....