My period usually lasts about a week. im REALLY STRESSED OUT

So i took a preggo test and it came out negative! Im still worried though because it was a dollar store test. even though it said 90 something percent acurate. And the whole period thing! when i took the test i wasnt on my (period] . but than a couple hours after the test blood came again O.o im so worried.

My period is 2 days late and I think it's because I'm worried about being pregnant. How long would I have to go stress-free for my period to start again? Thank you.