Period late but basically impossible to be pregnant

Kimberley
So my period is a day late now and it's frustrating cos it's basically impossible for me to be pregnant unless my fertile window was early and straight and after my period. I didn't track anything this month and it's been a hard month with being in pain for a week and then finding out I had an appendicitis. They done a pregnancy test at the hospital like 2 weeks ago that came back negative but wouldn't that be too early to show anything anyway?