Really confused....

I'm really confused as to wether I'm pregnant or not. According to the glow app my period should have been on March 14 but I haven't had it yet, it's now the 18. I have cramping, feel neasuse, boobs are a little sore , lose of appetite. I did a pregnancy test yesterday morning and I got a BFN my fertile window was from Feb 23- March 1. I feel so frustrated...