How do i know when my period is actually coming? PLEASE COMMENT

I’ve had sex in July but I had a short period after so I don’t think I’m pregnant, but my period was due the 6th and it STILL hasn’t come. I’m super worried and I hope its just the stress that is making me not have my period, but ive been cramping and I’ve been sore down there? I don’t know what’s going on, and I can’t handle to be pregnant, I’m 16. How can I relax and how can I make my period come faster???