Spotting?

Hey sooo....I have some questions and hopefully some of you may have answers. Im 21 and I'm sexually active, I started taking birth control pills on the 1st of November. From then until now, I missed one pill (sometime last week) but took pills accordingly after. For the past three days though, I realize I've been spotting only at night? During the day I'm fine but I realize it happens a few times only in the evening (TMI: it's not red or bloody, it's just brown). Only once I had minor cramps. I'm not due for my period for another two weeks and I'm not sure what could be causing this. I'm very healthy and my boyfriend and I have safe sex. Could this be a side affect from my pill? I was previously on the pill before but never experienced spotting like this.