What is the ruling on the yellowish discharge seen before and after menstruation? Is it considered menstruation? And is ghusl obligatory after the fifteenth day of seeing it?

We have explained the scholarly disagreement regarding yellowish and brownish discharges and have favored the Hanbali madhhab, which considers them menstruation if they occur during the usual period, and not menstruation otherwise.

If a woman experiences purity and then sees yellowish or brownish discharge, it is considered menstruation if it occurs during her usual period, and irregular bleeding (istihada) if it occurs after her usual period.

Similarly, any yellowish or brownish discharge a woman sees before the onset of menstruation is not considered menstruation.

What you are doing is not correct. You should not pay attention to yellowish or brownish discharge after achieving purity and after your usual period has ended. You must make up all the prayers you missed, thinking they were due to menstruation, because they are a debt upon you.

A Muslim must refer to people of knowledge for what is unclear to them.