Thanks for the query.
Usually the blood test
give accurate results in pregnancy
compared with urine test.
And of-course sometimes that can also give false negatives but that is rare.
So now what you can do is:
-Go for ultrasound
rule out the pregnancy and take the tablets or
-Use micronized progesterone
which are less harmful to the fetus.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429