I had about a 30 day cycle and I started BDing on CD 10 and would go every other day (or try to stick to it) and go up until CD 18. That way our bases were covered. Because I would usually ovulate on CD 15 or 16.
the most fertile days is the day before ovulation and the day you ovulate.
It does depend on ho0w long your cycle is. I had a 26-28 day cycle, so we started on CD10 - CD 16. The most fertile days are around 2 days prior to ovulation, day of ovulation and the day after. When I got pregnant with my daughter, we had intercourse the day before ovulation. Do you have the ovulation tests? Once they start turning up positive, then take advantage and TTC especially on those days.
Best of luck!!