late period

I've been using Glow for the past few months and once I finally got everything worked out properly it's been keeping track of my cycle pretty good. it said mine. Was supposed to start Sunday or at least was predicted which the past couple of months has been on a Sunday. I have not started it yet and a friend of mine told me that stress could stop me from having a period. in the so many years that I have been having a. I don't ever remember missing one because I was stressed out. anyway I took a pregnancy test and it was negative so I don't know. what should I do? last time I had a child was 9 years ago so I've kind of Forgotten what it's like to be pregnant.