Pregnant with IUD

Anyone else get pregnant with a IUD? Didn't even think to test till all sudden was feeling nauseous and very sensitive to smells and all sudden couldn't drink water! And then it hit me..this is exactly how I get when Im pregnant! Got two positive tests. And then I started to freak out! My baby is only 6 months old! Made a appointment at my OB . Definitely pregnant.. Either my IUD has disappeared somewhere or it fell out.. I just can't figure out how it could fall out without me feeling it! Just wondering if there's any other that this has happened to?