Dying, hunch back pullets

[Raisetherooster]

Why are my 8 week old chickens holding themselves like this? Back hunched, tail feathers down. The yellow one stood like that yesterday and was dead by this morning. Today, my olive egger is standing the same way. I attached a picture of my chicken with normal posture for comparison. I don’t know what I’m doing wrong. Fresh water and the best feed daily, and I have a really good set up that they live in. 12by15 run and a raised well ventilated coop made for 16 birds (I had 7)
Please help, I’m desperate!!

 

[Eggcessive]

Sorry for you loss. What do their poops look like? At their age, I would worry about possible coccidiosis so I would get some Corid right away. Dosage is 2 tsp (10 ml) of the liquid, or 1.5 tsp of the powder per gallon of water for 5 to 7 days. You can also give each one 1/2 tsp of the undiluted Corid orally every day in addition to the treated liquid. If you can send in a body, kept cold but not frozen, to your state vet for a necropsy, that could confirm coccidiosis. Here is a list of all state vets to contact:
https://www.metzerfarms.com/poultry-labs.html