Positive then negative??

Mae

I am currently on CD 37 Of 31 of a typically very regular cycle. A day after my missed period I took a FRER test and got a negative. Yesterday afternoon, which would have been 5 days after missed period I decided to take another one and I got a very faint positive. I took another test this morning with FMU expecting it to be darker but I think it’s negative. No sign of Af coming

Has this happened to anyone?