Starting birth control ?

I have been trying to get started on my Ortho Tri Cyclen Lo for a couple weeks, but my period has yet to come. I guess it's what you'd consider late (since I haven't been on the pill, my periods have been irregular). 1) I took Plan B a few weeks ago and my doctor said that is probably causing my period to not have arrived yet. Also, I have taken two pregnancy tests just to be sure, and they have been negative, so I'm not worried that I'm pregnant. Anyway, I'm anxious to start taking the pill with the Sunday start, but obviously since my period hasn't come, I haven't taken it. What are the effects/consequences if I take it on a Sunday even if I'm still waiting for my period? Thanks!