What is the ruling on blood that came down after 15 days from menstruation, and continued for five days, knowing that I am taking medication for endometriosis, and is this blood considered menstruation that prevents prayer?

If a woman sees blood after fifteen days from the cessation of the previous bleeding, it is a new menstrual period. However, if she sees it less than thirteen days after the cessation of the previous bleeding, and the total duration of both bleedings exceeds fifteen days, then it is irregular bleeding (istihada).