I have a 2 1/2 year old Production Red that all of a sudden has started laying thin shelled eggs. (plenty of oyster shell available) She has always laid eggs with strong shells until now. If I tap the shell at the pointy end with my fingernail, it cracks. I've also noticed her egg production has slacked off, she's laying 3 a week now. Has anyone else experienced this? Is this the start of problems, like internal laying? She's fine otherwise, healthy, runs around, comes for treats, eating fine, etc.