IUD help

I have an IUD, I still have a small period every month. I have heard of people getting pregnant with them. This month I have just had a couple spotting episodes and nothing else. I have been moody and very horny. I am married so it's not a big deal or anything but I have been paranoid and tested in the past, so I don't want to waste the money. What do you guys think. Just period or could it be implantation bleeding?