So being a girl ain't easy. Let's go through some basic maths:
7 days a month - PMS
7 days a month - Cramps and general period shenanigans
That leaves only 2 weeks a month of relative sanity and pain-free existence.
4 days you feel fat or ugly or have a huge spot in the middle of your forehead or hair that resembles a broom
3 days you have nothing to wear
2 days you are in generic bad mood because of the weather or your payslip or some other external force
3 days you are hungover
That leaves just 2 days of pretty, cheerful, pain-free, glamorous, well-dressed, sober you.
And you can bet you will be working on those days.