Missed period high temps... negative test!

I took a pregnancy test on day 38 and got a negative... I am late for my period by a lot! I’m never late! My bbt chart looked high then dipped and went high again does anyone know what this may mean? I’m not stressed or doing anything unusual that I can think of! I can’t really find any answers to why it would dip and rise again! And I have no period and a negative test 🤷🏼‍♀️🤷🏼‍♀️