Must I perform ghusl and make up the prayers if a brownish discharge appears on the eighth day after my period, knowing that the sign of purity is dryness, and I did not see it on the seventh day?

The maximum period for menstruation is fifteen days. Any blood, yellowish discharge, or brownish discharge seen during this period is considered menstruation.

One must not perform ghusl (ritual purification bath) until one sees one of the two signs of purity: dryness or the white discharge (al-qassah al-bayda’). As long as blood, or anything connected to it like yellowish or brownish discharge, is present within the menstrual period, the woman is in a state of menstruation.