Possible Pregnancy?

I'm not exactly sure if this is the correct forum to post in, but it seemed closest to the issue I am having at the moment.
My period is very regular, especially in the last year or so. This month, however, it was ten days late. It wasn't very heavy on the first day but the two days following it was even lighter, almost no blood. My periods normally last six days, but this month it was only three.
I took a pregnancy test the day after my period was late, and again about a week later, and both were negative. Is it possible that I am pregnant? Are there any other possibilities?
Thanks so much!