4 weeks and no period after switching from Qlaira to Yaz?

Why is this that i have not gotten my period yet? I switched Qlaira because my period would come randomly, in little bits. So right after i finished the package of qlaira my doctor told me to change to yaz right away (not wait for my next period). I am worried of when i will get it, since i feel like i should have gotten my period in the past weekend and even up to today. My final question is if I can have sex and not worry about getting pregnant at this stage. If my boyfriend does not need to use condoms????!? And if if still, then when can we not? Thanks xx