Help!

I need help I need help to understand my last period was September 16-20 my fertile window was September 28-October 4 my cycle length for this period is 31 so it’s saying I ovulated October 3 .. 31-14‎ = 17 so I basically ovulated on day 17 but here’s the confusing part I use 2 apps to keep track of my period the glow app it’s telling me my cycle length is 31 in on my other app it’s telling me my length is 38 so 38-14=24 so it’s saying I ovulate on day 24 on the app it’s just very confusing on the glow app my next period not due until October 17 in on the other app my period not due until October 24 so can someone explain to me which one is right in if I am pregnant I’ll be ok guessing 2 weeks 5 days as of rn it’s telling me to test in 7 more days but I just don’t know which one is my cycle length to understand my last period was September 16-20 my fertile window was September 28-October 4 my cycle length for this period is 31 so it’s saying I ovulated October 3 .. 31-14‎ = 17 so I basically ovulated on day 17 but here’s the confusing part I use 2 apps to keep track of my period the glow app it’s telling me my cycle length is 31 in on my other app it’s telling me my length is 38 so 38-14=24 so it’s saying I ovulate on day 24 on the app it’s just very confusing on the glow app my next period not due until October 17 in on the other app my period not due until October 24 so can someone explain to me which one is right in if I am pregnant I’ll be ok guessing 2 weeks 5 days as of rn it’s telling me to test in 7 more days but I just don’t know which one is my cycle length what do y’all think ?!