What is the ruling regarding a woman not knowing the number of days of her menstruation, with some numbers recurring non-consecutively? And are the discharges that appear after purification, which are yellowish or white, considered part of menstruation?

What we advise you to do is to turn away from whisperings (waswas) and not pay attention to them. Yellowish discharges connected with blood, or not connected with it but occurring during the period of menstruation, are considered menses. However, if you see them after the cessation of menstruation, and you do not see them at a time you are certain is your habitual period, then they are not considered menses, and for them, it suffices for you to perform istinja (definition) (washing the private parts) and wudu (ablution).