That sounds like you expelled it. From what I've heard, if that was to happen, it would normally happen shortly after installation...you are 5 months post-instal. I've heard that some women actually pass it in a blood clot. I'm sorry this happened to you...hopefully everything will be ok at the Dr's tomorrow.
That just happened to me and my body was expelling it. I hope you are feeling better. Sorry you are going through this too.
I had mine put in on December 12, 2008, and expelled it yesterday (April 26, 2009) after a long bout of severe cramping. Also would like to mention that it is now day 14 of my period, showing no signs of stopping.
Also would like to report a weight gain of about 20 lbs and a constant bloated feeling (and appearance). I have gone up three jean sizes and my body-confidence level is at an all-time low.
I didn't originally want the IUD, but my iron level has been at 70 for at least 6-9 months, so the doctor talked me into it.
I'm now glad that it's out! Hopefully I can lose some of the bloat before summer.