M.M.
Give it a few more days and take another test. Pregnancy test are very good these days. An HCG level is an HCG level. Depending on what type of IUD you have can effect your hormone levels. Some are hormone free others are not. Also know (touchy subject but true); an IUD does not stop conception. It stops implantation. Once in a while a little determined fertilized egg decides it does not care about that "darn IUD" and will implant anyway (those darn little buggers), but for the most part IUDs work well. I do not know what symptoms your body is giving you, but many pregnancy symptoms can present from hormonal shifts in your body on a normal swing. Give it a few days, retest and see what that gives you. Good Luck.