bloating with a black bloody discharge and constant ache like period pains.

for the last 4 months i have suffered from a bloody black/ dark brown discharge which last for the time between periods, i also get bloating all the time and period like pains which are constantly there. i have a coil in which will last for 10 years and i had this put in 9 months ago, the dr that put this in has since checked the coil as has my gp and this isnt thr cause of my problem. im due to see a specialist in 3 weeks for a scan and stuff but im scared i have cancer, what could it be