Pregnancy or prometrium delay ?

So I was recommended to start taking my progesterone supplements at 3 DPO because I have a history of recurrent losses. I believe that taking it as soon as I get a positive is too late, so they suggested that I take it at 3 DPO. However, I have no idea if I’m pregnant or not. My period is supposed to start today, but it hasn’t started yet, and I heard that progesterone delays the period. I’ve taken a pregnancy test, but it’s negative. My test has always been positive my missed period days if I was pregnant so I have no idea if I am or it’s just the progesterone supplements. Has anyone else had this issue ?