Not sure when AF is due, unsure of my cycle length

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According to Glow and another <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">period tracker</a> app AF is due 3/16, but I'm not sure how long my cycle is. I have never tracked my period before so I don't really have anything to compare it to. I feel like I may have had some early pregnancy signs and took 3 hpt all BFN!! I feel like I'm going crazy!!!