Please Help!

Can anyone help me please.  I stopped taking birth control on January 16, got AF the 19.  Then on February 15 I got AF again right on schedule and as long as it has always been.  This month I will be 4 days late tomorrow.  I've been really tired, a little nauseous, little dizzy, I've been having lower back pain and light cramping.  I've taken 3 tests and all have come out BFN!  Has this happened to anyone else?