I'm scared??!

My period was suppose to start yesterday apparently. I used a bunch of period trackers and apps to make sure if all of them where the same or not. All of them ay that my period was suppose to start  on the 28 and 29 but it hasn't today is the 30th of dec and idk if it's Bc of the month day changes since we have a 31st now but I'm getting super scared bc I'm thinking if I'm pregnant. I haven't had any symptoms that I've noticed  or any implantation bleeding. The only one thing I am going through is my boobs feel bigger and my nipples are itchy. My breast do not hurt. But my nipples feel irritated. I just really don't know what to do. I'm scared and I'm only 16. My last period occurred on nov 30 in the afternoon and last 6 days