Conception happens in the several hours after ovulation. Two (2) days before and after the ovulation are considered the most "fertile" days.Ovulation (egg-cell expulsion) usually occurs 14 days before the next menstrual period is due. For women with a 28-day long cycle, ovulation happens in the middle of the cycle. You can predict ovulation in a 3 ways:

1. The Calendar method - can be used only for women with regular cycles (like you). You can have intensive sex 16-12 days before the next period comes;
2. Measuring the body temperature – several hours after ovulation the body temperature raises a little, and you've got a "green light" for a healthy conception environment
3. Ovulation predictor tests- several hours before ovulation, luteinisating hormone (LH) makes a peak that can be detected with a special urine tests.

In your case (no pregnancy for more than a year of trying) it is possible that you or your aprtner are experiencing sterility and you need medical attention. You can consult your gynecologist. Your partner should be tested first and then you.