Brown discharge in place of AF

Sorry may be slightly TMI- I was wondering if anyone has been in a similar situation. My period was a couple of days late but had several BFN. I have PCOS but af always arrives 14 days after a positive opk. When it finally arrived (16dpo), or so I thought, it was only brown spotting- very light- and it has been the same for two days now. I know brown discharge means old blood, but my period is always really heavy and bright red from day one so don't know why this one is different. Anyone had a similar experience?