Understanding Positive Pregnancy Test with Normal Urine & Negative Blood Test

Question
20 years old, no kids and first date of last period Aug. 31, 2005:
Hello, about 2 weeks ago I though I got my monthly cycle. SO I did what I normally do and went to sleep. The next morning to my surprise I no longer had it. The next morning i took a hpt and it came back positive. So I took 2 more and they all came back with the same response. I have classic symptoms of pregnancy and everything. I went to my primary doctor since my ob couldnt see me for another 2 weeks. She took blood and urged the ob to see me the next day to make sure everything was ok. I went to the ob the next day and after her exam she said everything seemed fine. She also took blood. However my primary called me yesterday to say that she doesn't know what is going on but the lab came back negative for pregnancy. I am very worried and confused. I definately feel pregnant. Now I am playing phone tag with my ob's nurse and she said that I can't have a u/s til Nove.1 I feel that is too late. Should I be worried, has anyone heard of this before, should I just go to the ER and get an u/s there?  

Answer
There is no reason to go to the ER unless you have severe pain on one side of your abdomen or the other. A sonogram would not show any pregnancy until, at least, 6 weeks from the first day of your last period. The best bet would be to take two blood tests for pregnancy (Beta HCG) 48 hours apart. If there is a doubling of the results in 48 hours, it indicates a viable pregnancy. If there is a halving of the results in 48 hours, it indicates a miscarriage. if both results are less than 5, you were never pregnant.