Nexplanon

Ally
I got Nexplanon put into my arm on July 29th. When I was there my period hadnt started so they gave me a pregnancy test and it came back negative. I have not yet started my period and <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> says I'm 25 days late. I've had unprotected sex with my boyfriend a few times. Should I be worried?