Is it permissible for me to pray, fast, and perform Umrah if my menstrual cycle is irregular, and sometimes I see a light brownish or yellowish discharge accompanied by back pain, especially since I am an unmarried girl?

"Yellowish and brownish discharges are considered menstruation by the majority of scholars if their combined duration reaches a day and a night. They are not considered menstruation if they do not reach that duration, because the minimum period of menstruation according to them is a day and a night. As for the Hanbalis, they believe that yellowish and brownish discharges are not considered menstruation unless they occur within the customary period or are connected to blood. There is no harm in adopting the view of the majority. It is necessary to differentiate between yellowish and brownish discharges and the pure vaginal discharges, which, although pure, invalidate ablution."