I live in MN and I have 4 chickens and about 2 months ago 3 of my chickens stopped laying eggs. Now today they all stopped laying. I don’t know what’s wrong with them? I have them close to the house being it’s winter time. They have a heat light in there nesting box area. I changed there food gradually for higher protein, they get corn and dried worms every day. What can I do or what needs to be done to help them?