Bleeding During Sex

Ahna
my boyfriend and I had sex the other night, he came in me, and when he pulled out everything was bright red. we checked his penis for any cuts and didn't see anything. I'm not expecting my period for another week, however we have period sex and it's always been a dark reddish/brown, not literally fire red. I haven't spotted or anything since then so I have no idea what tf it could be?? I have an IUD and I'm a little worried about it, but like i said i haven't bled since, and I'm not in any pain. 
any possible ideas? should i just not worry?