Bleeding while having the coil

So I have the coil In have done for 2.5 years.

2 days who me and my partner had sex and he has said to me after he thinks I’m coming on... as there was blood
so I went to the toilet and when I wiped there was fresh red blood on tissue.
after that there was nothing there and still haven’t bled anymore 

does anyone know why?
i haven’t kept track of my periods since having the coil.