AF ONE DAY LATE

My AF is one day late but I've never been late in the years I've had a period... I was suppose to start on the 21st and nothing... About 2 weeks ago I was feeling what I thought was pms symptoms but now just my lower back hurts and I have heartburn... My breast don't hurt or feel tender they're just swollen ( which is hard to tell considering I'm a 36 DD) and I am experience cramps they're not super painful and I normally don't have cramps when my AF comes to town... Hmm could I be pregnant or am I over reacting?