Positive test followed by negative

picklesplus2

Hi!  A couple nights ago, I took a First Response and got a faint line.  I took another test the next evening and got a negative.  Has this ever happened to anyone?  I should be getting my period around the 13th.  I keep reading that a line is a line and there's no way it would show at all if I wasn't pregnant and that false positives are very rare.  I'm trying to relax, give it a few days, and not obsess, but that's easier said than done!