when can i take a pregnancy test if im irregular?

jackie

on feb , i got my period on the 17th , on march i had it the 12th, i had sex on my last day of my period, and for them past 2 weeks i havent been using protection so basically he cums inside , last monday i had some very light spotting with discharge and it just lasted for a lil bit,im guessing is implantion bleeding and now Idk when to test ? if my period is due tomorrow ? Idk , i dont want to go ahead and buy a test and get a false negative ...