Letting him ejaculate in me while on Birth Control.

Two months ago I got on Birth Control,I have two alarms on 3:30PM and 7:30PM I take them either one of those times. If I forget a day I will take the pill the next day. I never forget two pills in a row. Friday,Saturday and Sunday I let my boyfriend of 3 years ejaculate in me. I have 11 days left in my birth control pack and I've been having lower cramps. I'm just wondering what's the chance of pregnancy? I'm a smoker also. I've never been having cramps but since Sunday-Monday!