What breed, age, protein % of their feed, weather where you are, housing ...that would give enough information to start the guessing.
My Pekin & Japanese bantam do not lay egg in the whole of winter, my standard size hens some do lay egg, but far and few in between.
My Wyandotte hens do not lay egg in winter at all. They only do it in spring and summer.
Generally, most chickens do not lay egg in winter, it is the time their body take a break. A break that give their body to recover, rest and recharge. It is a well earned break.
The manufacture that produce the feed I got for my chickens increases feed protein to 17.5% in winter and back down to 17% in summer. The increase in protein boost their egg laying, but I don't know by how much.
Their age and breed also a factor as well. Older hen reduce their egg laying no matter what season. Molting is no egg production.