Confused

I have five different fertility apps on my phone and all of them give me a different date I'm suppose to start my period and I have entered the same info on all of them. Glow says I should start today but it's a no show and the longest date that shows me starting is 7 more days so do y'all think it's just too early to be testing. Got a positive opk on cd 25 and lasted four days so should I just go by my pos opk