Pregnancy with IUD?

I have an IUD got it in Jan of 2007 after having my second child.... The end of december and first of January I started getting sick on my stomach every single night which has went from that to an all day thing now. My boobs for a month were so sore and swollen I never thought pregnancy was a possibility due to me having the iud. I got online and started researching and then thought OMG what if? well I was super bloated up until a few weeks ago and my boobs quit hurting and went back down to size.... 30 or so pregnancy test later still NEG I have 3 faint positives in January went to clinic and got blood test that said NEG. For the past two weeks mostly when I lay down at night I have movement in my lower stomach sometimes it feels like flutters and sometimes it feels like a wave going across the bottom of my stomach. So I went to my Gyno for my Pap on Tues which was 3 days ago and told him I wanted the IUD out because I can only figure that its what is making me feel like im pregnant over the past few months so he goes in with several different tools but cant find my iud. I had to see another doctor the following day and he dug around and still no sign of it. I now have to have a ultrasound and go from there and be put to sleep to have it removed. I cant understand if all my preg test are negative why i have all this movement going on in the bottom part of my stomach. I calculated "IF" i were I would be right around 18 weeks. I already have two other children ages 5 and 3. I just dont know what is going on with me and would like any input or advice??