What is the ruling if menstrual blood exceeds fifteen days, and there is no regular period, but it is distinguishable as menstrual blood by its thickness and odor?

If the bleeding exceeds fifteen days, you are in a state of istihadah (definition) (non-menstrual bleeding), and you must rely on valid discrimination if there is no established habit. This means that menstruation should not be less than one day and one night, nor more than fifteen days. Discrimination is made by distinguishing between the thickness and lightness of the blood, or by its odor. There is no sin upon you for missing prayers due to your assumption of menstruation, as Allah overlooks mistakes. However, you must make up the prayers you missed, according to the majority of scholars.