Hmmm... Could it be stress

☆Heather June☆
Hey ladies, I have a question. I have a regular cycle but it does vary how many days. Anywhere from 28-31.  Closer to 29/30. And what do u know she hasn't shown her face. And I wake up with her starting to begin. 
​I feel crampy but nothing like period cramps. And it feels very moist/wet below, so I go to the bathroom and nothing; I wipe and nothing no red brown nothing. I have taken pg tests and all come back neg so is it safe I assume that I'm not pregnant?
​Help please. 
​* I also have two children when pg with them it showed the day of my period was to start right away!