Is the brown discharge that appeared five days before menstruation considered menstruation, allowing for breaking the fast in Ramadan and continuing to do so until purification?

The discharge you saw was a brownish discharge (kudra), and it is not considered menstruation outside of the regular time of menstruation. You should not have stopped fasting and praying except upon seeing blood. You are required to make up the days you broke your fast, and it is more prudent to also make up the prayers you missed.