Thoughts? 12dpo but bfn on frer

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2nd month ttc, 1st month temping and using Preseed. Only symptom I have had is nausea for the last 2 days. Been using amazon cheap tests which have all been negative. Temp went up again today and it’s our 4th wedding anniversary so I was hopeful and took frer - bfn. I know I’m not out til af shows but anyone have similar negative tests but high temps and still get bfp? Af is due Sunday.