Re: Menstral cycle
When I was younger, my periods came like clockwork, every 21-23 days, and lasted for 7 days. On the rare occasions when it was late or early, it was because of some great emotional upheaval in my life. Emotions can affect the hormones.
My periods became much more irregular starting with the age of 39, which I finally figured out was the start of the perimenopause years for me. Age can affect the hormones.
THere are other reasons, such as thyroid problems, but emotions and perimenopause are the two that I would first think of.