Help please!!

AF is three days late. I can’t tell you the last time time my period hasn’t been right on time. I am very regular, My left abdomen is cramping, my boobs are full and the nipple is darkening, I’ve kept a mild headache and my back is killing me. I’ve taken 5 tests in the past 3 days and they are all negative??! I don’t understand what’s going on. Help!