PLEASE HELP ME Am I pregnant?

I've been on necon 777 for over a year and I've been taking it very consistently, always within an hour or two of the same time to take it. Plus my boyfriend and I use condoms. Usually I take my first sugar pill Tuesday night, then my period will begin Thursday morning. My last period started super light Thursday afternoon. Maybe a week or so after my period I had brown discharge for a day, which my school nurse said was old blood and she said she didn't think I could be pregnant. It's Thursday night and my period is still not here. Should I be worried?