IUD fell out

I got my IUD placed end of June, and had a placement check 6 weeks after placemant. Everything looked good and placed correctly. My periods were shorter and lighter up till October. They got heavier but still only 4-5 days long. November comes and my period is now long but still heavy like October. My husband and I went on a getaway without the kids, which led to lots of sex. Lots of unprotected sex, which is what weve done since getting my IUD. Now right before christmas my period comes, or what I thought was my period. Started out just like any other time but as I get closer to the 6-7 day mark, my flow went from heavy to extreme heavy. I was bleeding through maxi pads in 2 hours and tampons in an hour. So on fast forward to day 10 (Tuesday), I'm checking for my strings because I'm worried now. As I feel for my strings, I think I felt the knot of the strings near my cervix. I left it alone and went on with my day. With New Years day being the following day, I didn't call the doctor. I am still bleeding very heavily this morning. I go to work as normal but notice my tampon is falling out from being full. I got to the bathroom to check on it and change it but as I'm on the toilet, I feel a large clot come out and i look in the toilet and see my IUD strings coming out of a very large clot or clump of tissue.im still bleeding and having large clots come.out and have been for a few days. Im going to call my doctor as its a lot of blood to lose and clot sizes being a concern. I am worried if I could be pregnant, having a miscarriage or having other issues.

Thoughts as to what might be going on?