I keep track of when I should be getting my period. I already tested myself with a pregnancy test when I was 4 days late. And again when it was 10 days late. Both tests where negative. Should I test one more time or what can be wrong?

I hate answering questions with questions, but sometimes it is necessary.

Are you testing using first morning urine?
Have you gained or lost a good bit of weight recently?
Under any undue stress?
Using any form of birth control? If so, what kind and for how long.