What Causes Brown Spotting Prior To Period?

HI
My wife has a regular 28 day period, always has typical brown spotting 4 days prior to period,2 days before period gets dark brown / black tar like discharge and on day 28 has her period. This month she has had pain in her back near ovaries at ovulation. After that lower back pain, dragging sensation in her lower abdoman. She took a first response test yesterday evening but due her period tomorrow. Still light brown spotting and only using a panty liner when normally has to use a pad due to increased levels. Could the test have been too early?