I have 12, almost 2 year old ISA brown chickens. It is June 12th and they are not laying like they should be. Only getting 3-5 eggs a day. They have stopped laying in the nesting box and are laying in a clean nest under the poop board. The nesting boxes are clean, I dont know why they have stopped laying. They are not moulting. I see no pests. They did better over the winter and there were at least 5-7 eggs a day. Just baffled. Could it be vitamins? I give them oyster shells too.