How are we not pregnant...?

My husband and I are trying for baby #3. My 6 year old son is not biologically his. But we have an 11 month old together. We tried for our daughter for over 2 years! After fertility testing and monitoring for me, we determined everything was fine with me.... So we had my husband tested and found that he had a bad morphology because of a varicocele. He had surgery to correct it and 6 months later, we were pregnant.

I got the Mirena IUD when our daughter was 9 weeks. Had it removed the first week of June and it brought on my first period shortly after. I allowed myself to have one full and regular cycle to get back on track before we actively started trying. We decided that we would not go crazy and try hard because it caused tension when we did that with our daughter. But we are making sure to BD every day. Yes, every day. I was already taking Prenatals and slightly exercising to help stay active. My husband is also extremely healthy and exercising everyday.... Even though we're not tracking ovulation or anything how can we miss it if we're BD everyday.... This is the 4th month AF came, should I be worried?

My husband is in the Army and is getting deployed in January, so this is our last month for almost a year to try! :-(