Even if your period is late for more than a month, it doesn’t seem likely that you are pregnant because your pregnancy test was negative. You may, however, be experiencing a functional ovarian cyst that produces hormones (estrogen) and delays the period. Such functional cysts usually exist for a few months and can cause a lapse of 2-3 periods, after which time a heavier period comes and a new cycle begins. An ovarian cyst can be diagnosed with an ultrasound. You can consult a gynecologist to follow up.