OK thanks makes sense thank you.I haven't heard of this. Are you fine with eating store-bought eggs?
I really don't know what could cause this, but my first thought would be the chickens' diet. In some groups I am in on facebook I occasionally see people asking about chicken food without certain ingredients they are sensitive to that are passed to the egg like kids with a severe corn or wheat allergy. They share research that has demonstrated that some of these things do indeed pass to the egg and eggs without certain things in their diet are ok for these people, but eggs from chickens that do consume the food the person is allergic to have caused reactions.
I don't have any first-hand experience with this at all, but this would be something I might consider looking into or at least change the chickens' diet up a bit and see how that went.