Naomi,

I used a OPK a week after the Dr said congirmed my pregnancy and that came up with a second line in fact it came up before the first line.

I've had faint lines on the run up to O and teh a couple of days after the dark line.

Have you done a OPK today ?
Eta i just re read your post. I would go and get a BT done to be sure what is going on and maybe also get a HPT. After what happend with your last lot of BT's could you not see a different Dr.

Also i think congratulations.