My period has been delayed by almost three weeks, but the pregnancy test is still negative. What does it mean?

There are many reasons why a woman can have missed periods. It's not always due to pregnancy. If you did not ovulate during that menstrual cycle, then your menses may be absent for that month. Other factors include stress and a poor diet. http://yourhealth.asiaone.com/content/missed-menses-not-pregnant