I think the sex got the bleeding started. It didn't last very long .
I spotted a little in the first few weeks but it was very light pink not bright red.
I don't think it IB but my cycle on the 27th was spotty and I am normally a heavy bleeder. So I'm thinking I got pregnant before my period came. I have never bled after sex.
I can't be implantation bleeding. Way to early.
That might be implantation i never had any noticable blood but it happens to other women. Also if it was rough sex you could have just over done it. :) good luck