Missed period but 9 negatives...?

I'm 6 weeks late.... I've been late before (2 or 3 months w/o period) I've taken 9 tests (4 EPT's...3 First Response...and 2 Clear Blue Digital) and they all have come up VERY negative. Not even the faintest positive. I waited to test about 3 weeks after my missed period...so I should be getting accurate results by now right?