What could be the reason for spotting between menstrual cycles?

exactly 14 days after the start of my last period i experienced 3 days of spotting. not heavy enough for even a slender tampon. it was panty shields only. the discharge was a thin mucus like texture, pinkish in color. i would have been due for my full period just under a week ago, so i am only a few days late. … or am i?