I recently had random vaginal bleeding that was not due to my period. When I did get my period that month, it was much lighter than usual. What could this mean?
Paul's suggestion of the MerelyMe's articles is a great one, and those should be really helpful. Bleeding between periods can be caused by a number of things, some related to pregnancy and some related to the female reproductive system that are important to be evaluated by a doctor.
Here are some links you might find helpful in addition to MerelyMe's pieces:
Everything You've Always Been Too Afraid to Ask the Gynocologist
Safe Sex and STDs
There are a number of reasons for bleeding in between your periods and you can read this article by Merely Me, a writer and community leader for this site, titled, Bleeding In Between Periods. What Does It Mean?
One other article, by Merely Me, which might help is called, Am I Pregnant? How to Know? Within that article is a mention and explanation of Implantation Bleeding, which may or may not apply to you.
If your normal period is more than a week late you can take a home pregnancy test, or be tested by a doctor. Those are the only two reliable ways to know if you are pregnant. Good luck to you.