How do you count your dpo???

Kailey • A girl in love with her hard working nurse • 3 angel babies & a Rainbow Baby Girl Hanalei! Pregnant with a second little miracle.
I've been counting mine since the LH surge and heavy ewcm (sometimes with spotting). 
Is that accurate??? Also if we have sex two days prior to this, my chances are still good?
Been ttc for over a year now and I'm wondering if I'm getting something wrong with my timing.