Late period

So I’ve had the Ovia app downloaded for some time now and track my period on that app. For a steady time now the app has been right at getting my period cycle on the dot. Start to finish. This month I was supposed to begin my period 3 days ago and still have not. The day i was supposed to begin my period i three up twice on a hike. I’ve taken 3, 1$ dollar pregnancy tests and they’ve all turned out negative. Do I need to invest in a more expensive test. Or should I not worry? I’m on birth control but we don’t use condoms. I need your help guys 😩