Brown discharge in middle of pill packet

Patient: I’m currently taking Microgynon birth control pill and have been for two years now. This has never happened before so I’m slightly worried. I’m in a sexually active relationship and I take my pill every day but the past couple of days I’ve noticed some brown spotting, the kind I usually get just before my period starts, however this time I have a week left on the pill before my period is due. I’ve read online that it’s both a sign of early pregnancy as well as a side-effect of taking birth control, what could it be?