I was not on birth control and it took my husband and I ten months of trying before I was able to get pregnant with my second child. I told myself in mid-September of that year that if I wasn't pregnant by Christmas, I was going to see a specialist. I became pregnant the next month; although, my declaration to myself had nothing to do with it.
There is a wonderful book out there that can help you understand every aspect of your cycle and help you figure out when you are most likely to become pregnant. The title is Taking Charge of Your Fertility: The Definitive Guide to Natural Birth Control, Pregnancy Achievement, and Reproductive Health. It is written by Toni Weschler. I thought it was a wonderful investment but you can probaby find it in your local library.
My teachers and mom had always told me that "you can get pregnant from having sex just once." What they never told me was how unlikely that is if the timing is not right.
I hope the book helps. In the meantime, try to relax and enjoy the process of trying to get pregnant. Good luck.