What Causes Delay In Periods?

Yes, I ave been on birth control (Byaz) for 5 years and last month I got off of it so i can try getting pregnant, typically after I get off my last pill of birth control I would have to wait 3-4 days until i get my period, well for the last month and this month i have been sexually active, and last month when i started my period i have a period tracker on my phone and clicked start when my period last month began, then i clicked end when it ended, well my next period (this month) was suppose to be 4 days ago and my phone says i am 4 days late, and i know i am late, i just want to know if there is a chance i could be pregnant, i don t want t have to take a pregnancy test right now, I m hoping you can tell me as to why i am late on my period and if its normal? Thanks!