When is the last time you took a pregnancy test?
You should probably head to the doctor to get a bloodtest.
If you aren't pregnant you'll need to find out what's going on!

There could be a million reasons why you haven't had a period if you recently took a negative pregnancy test. Maybe you are under alot of stress? That usually has alot to do with a late or absent period. If you think you're pregnant, test again. If its still negative, something could be wrong. I say make a doctor's appointment and see whats up.