I got pregnant on the pill, but it was because of antibiotics. If the pill has worked this long for you and you don't miss doses then the odds of being pregnant arn't really high. You could take a test just incase and let your dr know.
Good luck.
honestly, i dont think it is possible for you to be pregnant. i had similar issues in the past when on the pill for so many years. talk to your doctor if you are concerned. i talked to mine and he said that even if i did miss a pill or two, that after being on the pill so long that it wouldn't be a big enough opening for the possibility of pregnancy. after being on the pill for so long you stop ovulating (which occurs approx. 14 days after your first day of your last period, so usually mid cycle and not usually the week before your next expected period)
i would suggest that you take a look at your personal life, have you been stressed or really busy lately? have you been eating the same? have you started exercising, or stopped exercising? all these things can impact your period.
if you are really concerned feel free to buy a home pregnancy test and test. you can test whenever because you are already at your next expected period. (which you did have cause even a little bit of blood for a few days is your period) but if you are cheap (like me) you can just wait another month and see how that one goes. do whatever makes you comfortable. hope you're back to normal in no time. : )