Feeling down

Elizabeth • Hi im new to this app but I have two boys and last September I had a horrible miscarriage. Im trying to convince for about a year now. My boyfriend smokes alot so I`m not sure if it`s him.
I Don't know what is going on...... I have two children that r two years apart by my ex husband. They r now 4 and 6 years old. I had a terrible miscarriage in 2014. I have gotten myself check and everything came out good my other got himself check and he is also good. I had waited long enough to fully recover. So why haven't I gotten pregnant again? Am I doing something wrong or is that my health may be the problem? Or yet again maybe it's him? We would only have sex 6-8 times a month because he's always working. I don't know what it is. I'm feeling down about it.