If you temp orally I have heard it can make a difference, I temped vaginally and still got a drop so I suppose it is still possible, along with maybe broken sleep and other factors.

Do you know if your test is a sensitive one? Is it 10 or 20miu?
If you buy do one from the shop I highly recommend 'First Response' they are sold at Woolworths/Safeway, they are very sensitive and reliable.

Tomorrow should give you a better understanding anyway, if your temp continues to fall then things aren't looking so good but if they maintain or rise then you are still in with a good chance.