What is this? Miscarrige? Uterus lining? *TMI photos!!!*

Hi! So last night my bf and I had sex and he came in me, so I went to take a shower and clean my vagina after. In the shower this came out of me. I have the Mirena IUD and we are not trying to get pregnant. If this is a miscarriage (due to the fact that the Mirena could have stopped working), I'm concerned that I am going to get pregnant now since he came in me. I'm shocked, sad and concerned for the future as well. I bought Plan B just in case I should take it (is it safe to take the pill with Mirena?). I scheduled an appointment with my doctor but it's not until next week and it's difficult to wait. Also my boyfriend and I have "unprotected" sex all the time... meaning no condom but I have an IUD. I had brown spotting yesterday, and a light period started today. So, any advice on what this is and what to do?