Confused ...missed period from low carb or pgs??

I was due for my period last week, but all I got was some light spotting for a Day on, day off ....then nothing. I took a few tests but they were negative. I have been on a low carb diet change past month. Could that have something to do with no period? Or could it be an early pgs?? Has this happened to anyone? Not sure what to make of this.