Feeling confused !! Help Please !!!

Christina • I am 38 yrs old .... I have 4 kids whom I adore ... My husband & I have decided to try for a little girl !!!!
Ok so My Ovulation Date was Aug 15th, my hubby & I BD everyday that wknd ... I took a Pregnancy test last wk because the anticipation of the airing was driving me insane & it was a BFN ... 
On Monday I became very dizzy & light head resulting in me calling 911 because I almost passed out .. They said they took a blood test & the pregnancy test was negative.... AF is supposed to be due on Aug 30th which is Sunday .... However it's seems I AF came today 2 days early it is very light pink & creamy ... I have mild cramping & I don't wanna get my hopes up but I guess my question is ... How accurate are the Dr. Blood Pregnancy Test ???? 
I have been told pretty accurate but if still to early it can not show up even in the Blood Pregnancy Test !!!