late period, negative test

My period is over a week late now and I have taken a few pregnancy test, which came back negative. I had some cramping over a week ago that went away. I've had nausea and dizziness for the past two weeks or so. My period is alway regular, so I'm not sure what to make of this. After my second negative test I tried to stop thinking about it, thinking that maybe stressing myself out was making my period late, but still I've had nothing. None of my usual PMS symptoms and no spotting or anything. Any ideas? Should I try testing again?