It's normal for cycles to change after having children and also for them to change after beginning a new birth control. It may have been that you were having break through bleeding for the first several months and now the bleeding has stopped as your body has gotten used to the IUD, along with other possible reasons. Though if you are nervous about it, see your doctor for a blood test to see if you are pregnant or not. It's very unlikely to get pregnant with an IUD, unless it has slipped or fallen out, so you can see your doctor to make sure everything is going as it should.
Thanks AF showed up today :)