Did you use the same brand tests both times at home? It could be that the tests were not very reliable and both gave false positives ? It is just as likely though that the doctors was not realiable and thats why it was negative.

I see alot of people seem to get false positives, is this perhaps because of testing to early and the pregnancy not taking ? I have heard that this is actually quite common and that is only because we have the technology to test early that we now know this ?

Either way hope you get your BFP, will keep my fingers crossed for you.