All chickens generally need an adjustment time when temperatures begin to drop. It's normal. They may stay inside, shiver or huddle. Generally it takes around a week or so to them to acclimate to the new temperatures. Every drop may bring out the same behaviors.
I believe your feed is fine. Your housing may not be adequate. Prefab coops often lack insulation, and good ventilation. Don't close them up too tight as that will increase moisture and cause it to feel more cold. If you are where it freezes you could use straw bales around the outside of the coop to provide additional insulation. If you aren't where it freezes than bales can become rodent infested.
Also provide deeper bedding, and something to stand on out in the run to keep them off the ground. Hay, straw, or other bedding types.