Smoke free while pregnant?

First off I am 30 weeks pregnant and since January 2nd 2010 have not had one cigarette because of oral surgery and then because I found out I was indeed pregnant a few weeks later. Anyways I was coaxed into taking a Smoke Free Baby and Me cl in March by my mother because you get free diapers for a year if you don't smoke, I was against it because I had quit 21/2 months earlier and thought it unfair that I take advantage of a program to ist mothers who actually needed help but the nice mentor also talked me into taking it. Well yesterday I went in took the blow test for the carbon monoxide and it came out POSITIVE TWICE at a very minimal amount!!! I was shocked and irritated I told her I wanted to take the urine test thinking that the blow test needed re-calibrated but the urine test came out positive too!!! I do not live with smokers, I have not been out of the house to do anything since last May except grocery shopping and the essentials, I have not been around second hand smoke anywhere to my knowledge and I am most definitely confused. I now want to know how the hell I am getting carbon monoxide into my system and how to prevent it. I am so uptight about being healthy for this baby I don't drink soda, tea, coffee or eat chocolate because of caffeine. I don't want my baby to suffer in any way my only guess is my car has a leak some where I don't know please give me some suggestions....