Am I required to pray if dark blood continues to flow after my usual menstrual period, especially if there is pain similar to menstrual pain, and if the nature of the blood changes throughout the day?

The maximum duration of menstruation, according to the majority of scholars, is fifteen days, calculated from the total days of bleeding and any intervening periods of purity. If the bleeding does not exceed this duration, then all of it is considered menses, and the intervening purity is valid purity. However, if the bleeding exceeds this duration, then the woman is considered to be suffering from istihadah (non-menstrual vaginal bleeding).