What Causes Delayed Period While HPT Is Negative?

I had my last period on the 11th of March. I had protected sex on the 24th of March. I ve had a highly stressful month with overload of work and unpredictable hours of sleeping and eating. My period is late and I took a home pregnancy test today. The result was negative. I know stress can cause the period to be delayed but I m still a little worried. Can you help me?