Af question

Nicole • Expecting our first in March 2015!!!
Hey all...
​Need some help with this one! I am new to the tracking ovulation thing...including keeping track of my periods. The last few months I have need on an exactly 28 day cycle. This month, however, I am 7 days late for my period. I thought I started yesterday (had brown discharge which I'm assuming is old blood). Today I have nothing. No period, nothing. I have taken 4 pregnancy tests which all have been BFN. I did get sick last month but it was a short duration stomach bug. Anyone ever this late?!