3 days overdue

Hi, I have a question because I’m completely confused. I was supposed to get my period last Friday. This Monday morning, I took my temperature because I know what my temp is like in pregnancy—I’ve got 4 kids. But it’s low, 36.0. Why am I not getting my period? Or is it possible to have a low temp even if I normally run at 37 when pregnant? In my case. I still had a test at home, but it didn’t really work out—the first line came up faint and a bit off to the side, and no second line.