I suspect it is too early for a nesting box. When I first put mine in, I found pullets sleeping in the boxes. Then I had cleaning to do daily.
Find out the 'average' egging date for your breed and set the boxes no sooner than about a month early. That will give them time to get used to the nests without too long a wait for you. Also, it is a good idea to put fake "eggs" into the nests as a clue where they should lay their eggs. Some use golf balls, plastic eggs, wooden eggs, etc. The idea is to make the nesting box(es) look like a save place for layers.
My hens laid their first egg a good 4 months after hatching.