What Causes Vaginal Bleeding After Intercourse?

ive just had sex with my boyfriend and he said he felt something inside me, not so long ago i had the coil fitted and ive had constant period pains and bleeding since, i thought maybe i could feel it at one point when i was just sat down but my mum suggested it was because i knew it was there.. i stopped bleeding a few days ago and have started now straight after sex, im a little concerned