What Causes Delay In Period While Suffering From Anxiety?

Today is the second day ive missed my period. I suffer from major anxiety to the point it upsets my stomach. Last month i was really stressed out from school and worrying about being pregnant. I had sex 3 weeks ago with a condom and made him pull out. I m never late but I just have this weird feeling in my stomach. I took a test 2 days ago and It was negative but could it be too early? Did my anxiety cause me to be late for my period? Please help.