I am often stymied by questions at the doctors, because unless I am bleeding right that second, or have only just finished, I never know where I am in my cycle, and I don't even know if they're regular or not. I imagine I would be more aware if I were doing things where pregnancy was a possibility, but when I was I was on hormonal contraception and just trusted it to do its thing without keeping track.

Gosh, it'll be awful if it turns out to be true about swimming - I've been doing quite a bit of backstroke recently.