OPK CONFUSION

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Ok so...I just don't understand OPK anymore. It is so confusing. I was in my green zone last week, did OPKs every day.....the ONLY time I got a positive was with FMU which I don't think you're supposed to do. I got that positive then I tested again later in the day and not positive. So was that positive or not? Idk cause it was FMU...also when I selected that I got a positive in my <a href="https://play.google.com/store/apps/details?id=com.glow.android">glow app</a>, the app then marked that day as my O day...I thought a positive OPK means that O is coming the next day not the same day???? I'm using Wondfo tests by the way if it matters. Thanks in advance for your insight, ladies!