Is it normal to be late?

I have been dating my boyfriend for 6 months now. In March I was three days late on my period so I started on March 28 and ended on April 1. I was supposed to have another period on April 30 but now I'm 6 days late. My boyfriend and I have never had unprocted sex and he still pulls out just to be even more safe. He isn't worried because he says he knows nothing got in me but why haven't I started my period yet? Beging this late isn't normal for me.