What’s going on?

Been on Nexplanon for about a year and a half now. Stopped getting periods completely, no spotting no unusual discharge during this time up until today I wiped and light pink discharge was on the toilet paper.. I hadn’t had sex before that so it wasn’t from rough play or anything so I’m just confused. I actually have unprotected sex regularly & my boyfriend does finish in me very often but the birth control I have is supposed to be very effective? I took a test and I saw a very faint line but I don’t want to hype that line up bc it could very well be a evap line or the control line.. any ideas of what it could be?