Within every twenty eight day cycle our bodies experience ovulation and menstruation. Other cycles or patterns are also being repeated within us at the same time. American Dictionary of the English Language, Noah Webster, 1828. What is interesting about these two definitions is that the older one relates this function to nature. The other definition is simply clinical.
Menstruation usually has a negative connotation to it.
The time preceding it, PMS, is also portrayed negatively. It is simply looked at as the time when females are more emotional and irrational. When the egg is preparing itself for fertilization it is sending signals to the brain that it wants to get pregnant. It does not care if you think this is a good idea. This is not to say we should be dictated to by our bodies, but when we ignore the body's signals completely, the body can feel invalidated or angry.