My ovalation days were 19-20/09/12, had sex then and now my menses are her on the 3/10/12 with a 28-day cycle

So you were using body temp and professionally tracking your ovultation, thatye great, so many women come here using those silly phone or internet apps that are worthless, since women ovulate at various times not by certain number of days. So it is nice to hear from someone whs has taken the time and knows her ovulatoin dates.

But, it does not happen every time, some women may have to do this for months before they conceive,

Also remember that it's best to begin having intercourse about 2 days before your expected ovulation date.