No Period During Placebo Week

I've been using Marvelon BC for three months now and during January and February, my period always came on the second day of placebo week. For the month of March, I decided to not take the placebo pills altogether--which I know does not change anything since they are placebo pills. The problem is, I'm already on my second day but I still don't have my period. I have never missed a pill and I do not take any medications that could interfere with the BC. Any idea why this could be happening?