Understanding Blood Pregnancy Tests: Accuracy and What to Do

Question
I got my period back on Feb 9 I had a condom faliure on Feb 26.  I got plan b from my dr and took it on feb 28.  I got what I think was my period on March 9 it was the same amount of time as my normal periods.  However I have been feeling very bloated, my breast have been sore.  After taking several hpt's all negative I went to the dr and got a blood test on March 23 which was negative.  How accurate are the blood tests?

Thank you in advance for answering my question.

Answer
If your last period started on February 9, the earliest that you could have ovulated would have been February 22 and you could only have conceived if you had sex on February 21,22,23 or 24. The best time to take a pregnancy test is seven days after missing your next peiod.You were due for your next period on March 8. A blood test for pregnancy as well as a urine test for pregnancy is very accurate.