Bleeding after sex

Smilie • Hello our first baby girl is on the way on the 22nd November 2015... Please be a sticky baby 👼 ✨BD to all
So last night sex was feeling really tight but not sore and once we were finished I was bleeding bright red for a while, so I put a pad on since I wasn't hurting or cramping and put my heart doppler on and she was fine (21.1w) then this morning it's just bits of brown on my pad. I take it that's normal as it's old blood. Check my little princess again today and heart was still there.  We had sex that morning before it and I was fine...
I take it I've cut myself while having sex?