Side note: you might want to switch from layer feed since the extra calcium can cause issues in hens that aren't laying. I haven't used it even for my layers for a couple years because I have a lot of heritage breeds that don't lay a ton. I give them free choice oyster flakes and all-flock...
Old chickens don't lay very often. Chickens can live to be ten or even older but you're not going to get "spring chicken" productjon out of a 4 year old bird. Not a conspiracy, just nature.