Maybe oops..?

Bopper
Okay so this is my first cycle using <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> and I guessed when my last period started but I did have the correct day it finished on. Time rolls over and <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> has been telling me I should have my period for about 3-4 days now and I'm getting kinda worried. I am 18 and sexually active with my boyfriend however we ALWAYS use protection and we do know that it isn't always 100% reliable but that still doesn't mean this is concerning. If I still don't get my period soon I will go and buy a test. Any tips or times this has happened to anyone else?