Bleeding after sex

Erica

So my boyfriend and I have sex frequently and I never bleed. But last night we decided to have a quick one and I ended up bleeding. But it wasn’t a bright red, it was more of a muddy brown (which I know is old blood). I take my bc everyday and I don’t start my period for another 10 days. Is it possible I just wasn’t wet enough? Little freaked out because this doesn’t happen.