No Period for 8 months!

I have been on Loestrin since October of 2006. My periods were regular with this pill and I experienced no side effects. I noticed in June of 2007 my periods were becoming lighter and shorter. My last period was Dec. 1, 2007. I have had no spotting, bleeding, or any other indication of menstruation since that time. I am definitely not pregnant. I know it's not my body adjusting to the hormones since I have been on it for almost two years now. My doctor says it's fine, but I'm concerned. Should I be??