"Should I perform ghusl, or should I wait for the discharge to cease, while having doubts about my purity when I performed the previous ghusl due to the brownish discharge that was occurring? "

Praise be to Allah, and peace and blessings upon the Messenger of Allah, his family, and companions. To proceed:

Not seeing blood on the sanitary pad does not consider purity, but one must confirm the cessation of blood and what follows of yellow or brownish discharge. There are two signs of purity: the white discharge (white fluid) and dryness (the cotton or cloth comes out dry). Women's customs vary in this regard.

The yellow and brownish discharges take the ruling of menstruation if they occur during the menstrual period or are connected with menstrual blood. If a woman sees purity (either with the white discharge or dryness), she must perform Ghusl (ritual purification). If she does not see the white discharge, she relies on dryness, and it suffices to consider the external without the internal.

Performing Ghusl before seeing signs of purity is not valid, and it must be repeated upon seeing one of the two mentioned signs of purity.