It might be a little bit of blood from your period that's still being cleaned out. If it persists for two more days, it could be BV (esp if there's an odor).
Brown spotting is old blood. We will have this as a natural part of our body eliminating it or as part of a hormonal imbalance such as too much estrogen production. Bacterial vaginosis or BV isn't brown typically but a light watery discharge that is greyish in color with the hallmark of a very bad smell. Really, do not think this is anything to worry about as most women have brown spotting at times. If it continues mid cycle, talk to your doctor at your next pap smear and they will most likely do a hormone panel. good luck