Has anyone ever heard or read anything about hard egg shells? I'm beginning to wonder if this could be a possible reason why I haven't got my

yet. I have had the usual blood tests, dye tests, scans, and general poking and prodding, and DH has had two SA tests done, and hey presto! whaddya know? we're both normal.
Maybe I'm clutching at straws here, but why else could we not be pregnant. Maybe OH's swimmers are getting there but my shells are hard boiled....
Any thoughts ladies??
xx