14dpiui BFP and then BFN

I tested on a FRER last night and had a clear BFP. I triggered on September 18th. So, I tested again this morning on a clear blue digital and it was BFN. What's going on? Is it possible that I am PG but hasn't reflected the test yet? Maybe I am over analyzing this... Which is possibly true.... But this morning when I took the test it was not my FMU. I had emptied my bladder several times during the night.  I also dipped the test into the cup of urine (which was clear). Do you think this had an effect. All of a sudden I don't feel any of the symptoms I had felts over the past few days. I have a twinge of pain in my pelvic area and light headed ness here and there. No AF sings at all.  Suggestions?