Hmmm, I think the last time I had time off work for sickness was when I had flu in....I think it was 1997!!!!!!!! How many days off am I owed? I think I'll go on a world tour.
One thing Whirlygig didn't mention was that not all women have regular menstrual cycles. I'm not talking about a couple of days different either...how about anything from 21 to 35 days????!!!! OK, now try and work out when you're going to get lucky.