Cramps and brown discharge a week before period.?

I'm ttc, my period is due today but still nothing. Had cramps 6 days before period was due, it hurt when I walked too wich was kinda weird. Had brown discharge the next day. I've taken about four tests since then and they all come out negative. I haven't taken one today I figured i would wait till tomorrow. My stomach had been upset lately too, and have had frequent urination aswell. Could I be pregnant? Why do all the tests come out negative :(