Pregnancy

I've been with my boyfriend for a year well will be tomorrow , and we always have unprotected sex and have been for awhile. 6 months on birth control and 6 months off, I have no be able to get pregnant. I want to have a child. I am a smoker and as well is he . I have a little bit of weight on me and my periods are irregular. I didn't have my period for over two years but then I got on bc and my periods came. I still have my period while being off the pill but it's a few days late and it's light. Lasts about three days . I have no idea what is going on. I don't know why I can get pregnant. Any ideas on why it's not happening.? It makes me sad, I feel like I'll never be able to have kids.