Return of yellowish discharge and very slight traces of blood after the end of menstrual bleeding

How to distinguish between yellowish discharge and ordinary secretions?

Her sign of purity comes and goes, and she gets a yellowish discharge on the eleventh day

Does a menstruating woman have to change her clothes once her period ends?

She gets brownish spotting before the bleeding starts

Her menses ended but there is still some blood in the urine; should she fast?

Does she have to insert a piece of cotton to check whether her menses has ended, or is it sufficient to wait for twenty-four hours and then do ghusl?

Her period became irregular as a result of taking the pill; what should she do?