When's the earliest dpo....

When's the earliest dpo should I take a test. I'm not all that familiar of the whole dpo thing.This month only had a 4 day period which I've never had in my life 😆. Been trying for a little over a year to get pregnant n it seems to not be happening for me. I've had 2 miscarriages n a chemical. I'm gonna try my hardest to not take a test. Which is gonna kill me to not take one lol. Jus wanna kno when's the best time besides missing ur period to take a test. Thank u.