BFN too “early”?

Has anyone tested like 2 days after missed period and the test being BFN but then finding out later on that you’re pregnant?

I’m 2 days late and I’m never usually late. Felt cramping few days ago and sometimes nausea. I tested with the Walmart First Signal test and it was BFN. I know you’re “technically” supposed to test 1 week after missed period.

Has this happened to anyone where it was negative and then positive after the week?