Could I be pregnant?

I am currently on birth control (yasmin) and I'm pretty good for taking it at the same time every day, for the most part (I have a reminder set on my cell phone, which I lost a few weeks ago, it messed up my routine and I may have taken a few pills late)... my boyfriend and I never use condoms and he frequently finishes inside me... lately I've had lower abdominal stomach cramps that are mid-cycle (I am not expecting my period for a few weeks)... last friday I was sent home from work due to unexplained nausea in the a.m. ... should I be concerned? Could I be pregnant?