Regular periods till now. Spotting no period with IUD?

The Mirena can cause periods to stop, it releases a low level of synthetic progesterone. A copper IUD may cause periods to stop, but doesn't generally have this effect soon after placement.

Depending on the type of IUD and the length of time it has been in place - you may want to check in with the Doctor Who placed it to see if you need a pregnancy test. Generally if an IUD is going to fail it does so in the first 3 months.