DPO question

Hey all,

So DPO, meaning days past first day of ovulation window, or days since the end of the ovulation window, days since peak ovulation???

We have been trying for going on three years, with 1 daughter and 3 miscarriages. I am about 7 days from my projected period, and am having a ton of symptoms

(Dizzy, bloated, headaches, sinus congestion, insomnia, fatigue, tender/heavy breasts)...trying not to overthink, but also trying to figure out the earliest I could test...

Help please!