Help! I'm so confused.

C 💕
So we just started TTC this month, so I got this app. I put in all the same information (past periods, days we had sex, anything I put from another app I use called Flo.) I've been using that app for a few months and it's usually spot on, give or take a weird month when it's a day late. But otherwise it's pretty accurate. Both apps are telling me different days when I was supposed to ovulate. I didn't take an ovulation test because i figured my first app was right & I didn't notice they had different dates. So, according to Flo I ovulated three weeks ago. This one says I ovulated almost two weeks ago. The expected period dates were only two days apart, if I'm reading them correctly.   So I'm not sure how many dpo I actually am and when I should test. I've taken a few tests already since my period is definitely late. I know I can test every few days but I just want to know which one I should base my ovulation off of in case I'm not pregnant. I bough ovulation tests for next month, just in case but still. Any insight would e appreciated.