It can mean one of several things: First, you may be ovulating, but you may be one of the few women whose temperatures do not reflect the heat-inducing progesterone produced following ovulation. Second, you may indeed be having a thermal shift, but are not drawing the coverline correctly in order to accurately interpret your charts Third, and finally, you may not be ovulating altogether, although this is not that likely, since women with extremely regular cycles usually do ovulate.