I was like that with my first pg. I had every textbook symptom and kept getting -HPT's, and it took 2 BT's to confirm the pg. I was about 6 weeks before it was confirmed. So it is possible it is a little too early to tell, because my first BT came back inconclusive because there wasn't enough HCG to definately confirm a pg. I would go and have another blood test because if you are pg, the HCG levels would have risen heaps by now.

Good luck