What Causes A Missed Period After Having Sexual Intercourse?

hi i am 20 yr old unmarried girl.i am missing after having sexual intercourse with my boy friend on 5th of ths month.1st day of my last periods was on july 13th.am i pregnant?if so what to do for me to terminate it,without going to hospital.please help me.i can take any medication.not allergic to any drugs nor bleeding disorders