Has the menstrual period become more frequent after inserting the IUD, and should it be counted as 7 or 9 days, or should anything beyond that be considered istihadah (post-menstrual bleeding)?

If the blood discharged after the end of the menstrual period, regardless of its colors, differs from menstrual blood in color and smell, and the woman knows that this is due to the IUD, then it is irregular bleeding (istihadah) and does not prevent what menstrual blood prevents.