In the current scenario, I would ask for a trans-vaginal sonogram along with a blood test
to know the status. If pregnancy or any other pelvic pathology has been ruled out, you should test for blood profile as well as hormonal
imbalances. Any weight changes, stress and medications are also possible causes for the irregular menstrual pattern. If the IUD is found to be causing it, it needs to be removed and an alternate contraceptive
method planned. Hope this helps.