What Causes Delayed Period, Abdominal Cramping And Tiredness After Having Sex?

I need help, you see, my friends and I have the same period schedules. Mine is suppose to be here by the twenty first while theirs came on the 9th or so. We also had sex the day before I ended up ovulated. I ve been cramping, feeling sick, and also extremely tired for the past two weeks. Could I be pregnant or am I just worrying?