So confused

Ca

at first. it said my ovulation day was on the 13. so i started testing couple days before. I keep testing everyday, and ovulation keeps getting pushed back bc of the negative results. i understand the app is just an estimate, but am i really this far off? i thought you generally surged around 15 days after the start of your period. I just keep testing? The test line isn’t getting any darker with the days passing.