Lately, our hens started producing strange-looking eggs. They come with wrinkles and the shells are super hard. There is nothing wrong inside. I just wanted to see if we are doing something wrong to our hens or if they are sick. We've been feeding egg lay pellets (crumbled), scratch, flock raiser, oyster shells, and lately to help molting, feather growing food. These wrinkled eggs shells are super hard, but sometimes, they lay eggs with very thin. Just wanted to know if this is a strange thing and if so, what can I do to help? Any advise would be helpful. Thank you.