That's very common and nothing to worry about unless it continues for weeks
or gets MUCH heavier.
That brown discharge
is just blood that did not get expelled during your last period. When blood gets "old" it turns brown. As your uterus is now preparing for your next period, the old blood is finally being shed. It happens to ALL of us, trust me. We either take to wearing mini pads for a few days after our periods or buying LOTS of new panties! LOL
Please don't worry about it.