Hi. My Period Is Actually Due Tomorrow But It Started

Hi. My period is actually due tomorrow but it started on Thursday. Its not a heavy flow. Its light actually. When I take my tampon out its a mucusy dark and regular color blood on it...and it doesn't fill even half of the tampon so its light..I've been cramping a lot since it started,and have been having low back pain and constipation for almost a week. I have endured recent stress and also could be pregnant..please I need answers