should I be concerned?

hey guys, my calendar says I was supposed to start my period today, and usually a week before I start my breasts hurt. obviously I haven't started yet and my breasts aren't even the slightest bit sore, so I'm not sure when I'm supposed to get it. my periods have been on time for the past couple months, though I'm sexually acitve (but with a condom). I don't have any signs of pregnancy but since I'm only 19 it's one of my biggest fears. should I be concerned?