IUD Problem

I have had the Mirena IUD for 6 months now. At first, I didn’t have any problems except for the first couple of weeks and haven’t had my period since. In the last few weeks though, I’ve bled a ton and had awful cramping out of nowhere. Last night my husband and I had sex and after, I was doubled over in so much pain in my abdomen that I couldn’t even move. I felt like I was going to vomit, and was shaking from chills. Is this normal at all or has anyone experienced this while on the IUD? I also couldn’t feel my strings last night either so I’m wondering if it might be misplaced?