Hi There, I Have Been On Alesse 28 For About

Hi there, I have been on alesse 28 for about two years. For the last three days I have had a reddish brown discharge from my vagina. I am supposed to have my 'period' next week so I do not understand why this is happening to me. I am sexually active and do not use a condom. I would like to know the reason that I am having this discharge. Thanks in advance,

Anika