Late period and negative pregnancy test

So my period has been earlier past few months and it’s weird to see it come late this time. To give context ive done the deed with my bf but Istg it was no where near my ovulation window and we used protection ofc. I don’t use birth control btw. I could say my cycles ranges from 28-31 days but according to my tracking it’s late by 2/3 days now??? Kinda stressed now about being pregnant but I took two pregnancy tests - one this morning and they both came out negative ???? What could this be. So lost and confused ? Is the test false but I’m sure I’m not pregnant at all because I got no symptoms other than stiff back for a few Days / acne which points to PMS?