So I'm usually like clockwork for my cycles, but I've found myself to be 8 days late now. Two negative tests on Monday and Tuesday. Started spotting lightly after having a bowel movement (sorry tmi, but very constipated.) Bleeding is very light and appears to be old blood, comes and goes when going to the bathroom but not on the panty liner at all. Intense heaviness in pelvic area, and intermittent sharp pains. Could this be the beginning of a period or should I be worried enough to see my doctor?