FRER is wrong?

Kate • DS born 4/30/14 ~°~°~°~ DS#2 arriving April 21st!!

my last period was on March 4th, we DTD several times during my fertile cycle and I'm pretty sure I O'd on the 26th. I tested with only FRERs on the 6th, 8th, 12th and 15th of April all were negative. my cycles are always 36-39 days long except for this cycle which is going on day 43... I swear I'm pregnant but I'm not getting a BFP has anyone else used FRERs and not gotten a positive until after missing their period?