Sex, Plan B One Step, & Pregnancy Chances

Patient: I had unprotected sex (no ejaculation) 6 days before my period was due to start. (It’s usually 28-31 days between my cycles.) Within an hour of having the unprotected sex I took Plan B one step. What are the odds of me becoming pregnant, and when can I expect my next period to start? Thanks so much!

Symptoms: Slight to mild cramps, swollen breasts, extra tired, very mild headaches