Got IUD (mirena) & Missed period

This is my 3rd time getting the IUD. 1st time lasted 2 months then was removed because of wrong insertion . 2nd time I had for a year & a half and I always had my period . This time I’ve had the IUD for a little over 4 months and I’ve still had my period since it was placed and now my period is late .... this had never happened to me so I’m not sure if I should be concerned or not ...HELP!!!