Confusion on when to test?

So I ovulated on the 2nd of August, (positive OPK @ CD 20) so that makes me 10 days past ovulation, however glow is calculating my cycles to be an average of 39 days long which has my period not set to arrive for another 10 days!? Do I judge DPO to test or days before expected period? If I wait until my period is due I will actually be 20 DPO but if I test at even 14 DPO it will be nearly a week before my expected period. So confused. This will only be my second period post pill so my cycle is still working itself out.