the newer IUD's and coil's do that now the stop your periods or make them very very light
Ihad the mirena (which I do not recommennd) I had no periods after 2 months my friend had spotting the entire time she had her IUD which is just plan annoying. If your doctor is not worried then you should not be either.
As I said they use these for some women because it stops their periods or makes them lighter or because they haave issues with their blood for me I had the mirena put in because I developed lung clots medical term a P.E. pulemary embolise. You can talk to the pharmacy you purchased the IUD or any one for that matter just tell them the name and ask if this is a common effect of this IUD.
Unless you think you are pregnant. If that is the case go buy a test and see but your Dr should have tesed you before heésheput the IUD in.
Hope this eases your mind,
take care
tykare