Delayed Period & Negative Pregnancy Tests: What Could It Mean?

Question
I just turned 21 and have no children, I am in a monogomous relationship and we do not use birth control.  I have been off the pill for about five months and have had regular periods, where I knew what hour it was coming.  My last period started on Jan 26 of this year.  I have not had one since.  I have taken about  10 tests, and all have been negative.  About two weeks ago I went to the doctor.  She gave me a urine test that also came back negative and would not give me a blood test, she said it was just stress.  Could I still be pregnant?

Answer
If your normally have a 28 day cycle (from the first day of your period until the first day of your next period) ovulation occurs on cycle day #14. You can become pregnant if you have unprotected sex on cycle day #13, 14, 15, or 16. If your last period started on January 26, you would have ovulated on February 8 and could have conceived if you had sex on February 7,8,9, or 10. If you did become pregnant, a pregnancy test would not show a positive result until 14-21 days later. The best (most accurate) time to take a pregnancy test is seven days after missing your next period. You were due for your next period on February 22. Therefore a pregnancy test would be accurate after March 1. If you took 10 urine tests since March 1, and they were all negative, you are most likely not pregnant. You can take two blood tests (Beta HCG) for pregnancy. If both tests show a value of less than 5, you are definitely not pregnant. If there is a doubling of the results in 48 hours, it indicates pregnancy.If  the test is negative, you merely have some hormonal imbalance this month. See if you get your period around April 19. If you don't, demand to have a quantative HCG test and you will know for sure.