AF is late...

Totally freaking out! AF is late (three days) and when I selected that I'm late, my period date recalculated to later this week. Ok, no problem, but I'm never more than a 28 day cycle AND I just started seeing a new guy. I'm TERRIFIED that, although using protection, somehow the obvious happened. Has this happened to anyone else and AF was just later than usual!? Please help ease my racing mind!