it could possibly be the lubrication the dr used when she put the iud in. (?) is it clear, yellow, red? if its reddish color or rust color, its probably a little blood left over. i wouldnt worry too much about it. (but it still helps to know what that stuff is!)
I got my IUD a month ago and had the same thing happen. They said it was most likely the cleanser (it is brown/orange in color) they use to sterilize things before insertion and after a couple days it stopped.