Trying for over 1 year...Still nothing

My fiancé and I have been trying to get pregnant for over a year now. We never use protection yet we still are not having any luck. My mind plays tricks on me. I want to be a mommy so bad that my mind plays tricks on me and then I get discouraged when I take a test and it comes back negative. My fiancé is a smoker and is over weight. I am slightly over weight but want to lose weight. I'm just not sure what we are doing wrong and why we can't get pregnant. I'm not sure what to do to help us become pregnant. Any advice or tricks on how I can become a mommy would be great!!