What To Do After Missing Periods After Switching Birth Control Pills?

Hi! my name is Terri and i have a question about birth control pills. I am taking Yaz and last month the switched me over to a generic instead of the brand name. I had unprotected sex and then took the plan b one step pill a couple days ago. i havent gotten my period yet. I had already took all my "sugar" pills. What should i do? should i just go ahead and start a new pack of pills?