I often had a brown discharge: I would have very heavy, clotty period for 10-ish days, then a 2 day break B4 the brown staining for 24 hours. Normal for me. Probably due to not enough hormone to cleanse the womb completely, brown is blood that has been 'stuck.
However if there is an odour i.e. fishy, then it may be an infection or simply the old blood becoming stuck. The GP/Nurse should take a swab to check.