I need help, if anyone could help

I’ve been trying to get pregnant for a while now but seem like I can’t. I track my period on two apps which is P.C & Flow they both tell me when I ovulate but it’s two different dates so I’m not really sure which app i should go off of If someone could help please :). P.C is the one with ovulation on the 15th and Flow is the one that say Ovulation on the 13th