What Causes Brownish Vaginal Discharge When On Levlen?

Hi, I have been taking levlen ed for about 3months now. Last month I had my period for 2weeks (heavy period) and now There s brown blood on my panty liners. I usually get my period at the end of the month or the start of the month. Should I be worried about this brown blood? I haven t taken any of my sugar pills because I ve decided to miss my period this Feb.