IUDs don't prevent ovulation, they prevent implantation. So you could have ovulated and the sperm could have met the egg, and when the IUD left, they were ready to go. Spotting could just be a result of the IUD removal, but it is not impossible that it could be a pregnancy. So test two weeks after the sex.
nothing it just means you are having break through spotting from the removal, it takes a while for your body to regulate from the removal.