Did your body reject the IUD?

I had an Iud inserted less than a week ago and it already came out on its own. I was told that it could've been placed wrongly they first time or that my body could've rejected it. I really want to make the iud work for me, but the only way to know if my body rejects it is to try one more time. I'm not insured and these things are not cheap, so I'm trying to find some info from gals who have had a similar experience with this. Thanks girls