almost a month late but...

Deserez
So I'm almost an entire month late... which is exciting I guess, we've been trying for 6 almost 7 months now. I've taken two pregnancy tests in the past two weeks each saying negative... I'm worried now that maybe it won't ever happen... but after a month of no period... is there something that would cause a pregnancy test to not show positive? 
Note: the past week and a half I've been getting up early morning and late night between 2am to 9am super sick. The last test I took was 4 days ago.