Spotting a week before period

Jessica
Yesterday I got what I thought was an early period but it was extremely light and has been light all day now. This spotting has started a week before my period is supposed to come. I'm on birth control and have never kissed a pill and have always stayed within a 2 hour timeframe when taking the pill. Condoms have never broken during sex and my SO has never came inside of me. Is this normal? Could I be pregnant? I went to the wellness center at my school and took a pregnancy test but it was negative.