BFP THEN BFN??

So on Saturday AM (12dpo) I took a test and I thought I saw the faintest shadow of a line but put it down to my eyes so binned it. Sunday AM, there was a VERY faint line but defo something there (within the time limit). Monday AM and today AM, negative, bright white tests with not even the hint of a shadow. Period was due Sunday night/Monday morning (always starts during the night, always has done) yet not even the slightest hint of anything yet. What’s going on😭😭