What Are The Side Effects Of Mirena?

Hi, I am a 50 year old female, I have a mirena coil fitted. I use lubricant during sex, but do not have sex very often. When I have sex lose get red blood from the vagina, sometimes a lot sometimes a little, my doctors have told me to keep an eye, my smear tests are OK, although about 7 years ago I had treatment for irregular cells. Could the blood be due to my coil being incorrectly placed ?