Missed my period?

So my boyfriend and me have been together for over a year now and we had unprotected sex just 9 days before my period ( he pulled out )
But <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a> is saying that my period is 4 days late. But I usually don't get my periods until around the 12th-16th day of the month. Did I really skip a period or could <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a> be wrong..?