confused

I have 2 apps for tracking my cycle. Glow and Ovia. Glow I just started this past month, Ovia I have used since last December. Glow says that today is the end of my fertile window but Ovia says I am in my fertile window now! I don't know which to believe! I just started taking opk this week and haven't had a positive yet. I'm just so confused! Any help or advice would be greatly appreciated!!:)