I hah unprotected sex last feb 25. been stress for a week and got brown spot last feb 27 and now im 6 days late and had cramps. is it due to stress or?

Most common is...: If young, fertile, and having sex, a woman is on the highway to pregnancy... so the most common cause of a missed regular period would be pregnancy. First, she should check a preg. test. A urine test, done correctly, gives a reliable result 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. If not pregnant, there are other reasons for lateness.