How can one differentiate between menstrual blood, yellowish discharge, and brownish discharge in the absence of a regular monthly period, and what is the ruling regarding the prayers I missed?

It is clear that the questioner is afflicted with waswasah (obsessive whispering). Yellowish and brownish discharges (sufratu wa kudratu) are not considered menstruation unless they are connected to blood or occur during the usual period. If she sees blood and the yellowish and brownish discharges continue for more than fifteen days, then she is experiencing istihadah (non-menstrual vaginal bleeding), and she should not succumb to waswasah but rather adopt the easiest opinions to repel the waswasah and remove hardship.