One of my chickens (a 6mth old Light Sussex) has stopped laying and is spending a lot of time just sitting in the nesting box. Very strange behaviour for her as she usually runs around the garden with the kids, very sociable and friendly! I feed her spaghetti, boiled brown rice, potato, buckwheat,corn and some organic layers pellets.........a mixture of all. Is this normal or does she need a trip to the vets? Please help!!!