Open Question: question about Yaz, and when to start my next pack?

i'm taking yaz, the birth control pill, and i'm not sure when to start my next pack. yesterday was the last day of my last pack, but even though i got through all of the lighter colored pills, my period hasn't started yet. should i start the next pack tonight? when should i start it? why hasn't my period started? (it is literally impossible for me to be pregnant. i'm not even on the pill for birth control purposes)