no period after taking yaz and i am on my second to last day

I have been taking the pill for about 6 years, at my last checkup my doctor switched me to Yaz. I havent missed any pills and have taken them around the same time each day. I am at the end of the pill pack, only 2 pills left and so far i still havent gotten my period. This never happened when I was on my other pill. Is this normal or could I some how be pregnant?