Disclaimer:
I'm a 57-year-old single guy, with next to no knowledge of 'women's issues'!
However you might find this link useful:
http://www.nhs.uk/con...ges/Introduction.aspx
(Play the video and click through all of the links which are offered to you).
In particular, I note this quote from the 'Symptoms' page:
"In most cases, the first symptom is a change in the usual pattern of your periods. Your period may start every two to three weeks, or you may not have one for months at a time. The amount of menstrual blood lost may also change, and most women find it increases slightly".
Chris