Brown discharge before period. Normal?

I've been on the ocp ovral-l for 8 months now and have been extremely consistent and never missed a pill or even been late in starting a pack. My 21 pill pack for this month ends today on 6th August and my period usually comes 3 days after I stop the pills. But, my periods have been lighter the past 3 months and today I've noticed that my cervical mucus is showing small brown thread like structures in it. My periods haven't started yet as the due date is yet to come but im having this brown discharge and cramps as well. Should I be concerned of the chance of pregnancy here or is this normal? I've consistently taken homes pregnancy tests and even done blood pregnancy tests in the past 3 months, all of which were negative always. I have also never missed a period on the pill though it has become lighter. Plz do advise.