Are these secretions considered istihadah, how long is the menstrual period calculated to be, and is sexual intercourse permissible in this case?

Menstruation can increase, decrease, come early, or be delayed, especially with the use of contraceptives like the IUD. Purity is recognized by two signs: the emission of the white discharge (al-qassah al-bayḍāʾ), or complete dryness. Yellowish or brownish discharges connected to menstruation are considered part of menstruation unless the woman sees the white discharge or experiences complete dryness, even if it exceeds the usual days, provided that the menstruation does not exceed fifteen days; otherwise, it is considered irregular bleeding (istiḥāḍah). If the bleeding exceeds fifteen days, then in the following month, the woman should perform ghusl (ritual purification) and pray after the duration of her customary period, which has become established after the insertion of the IUD.