help needed for calculating dpo please :) ❤️

Katie
Hey guys, so as you know we have decided to start trying again. This time I'm tracking my ovulation using opks. 
Never done this before so need advice please :)
So since last Sunday I have had faint tests, on Thursday and Friday the tests were as dark as it th control line, then have gradually got fainter since Saturday and blank this morning (however tested early as woke up around 6am). 
What day do I count as days past ovulation.... the first day I got a faint line, the dark line I had, or from today which was blank (will test again when home)
Just as an extra note, when ovulating I have one sided pain, however yesterday I had period like pains but not as strong, like a pulling feeling? I have been bding every day since my first faint line.