Your fertile period is 7 days before and 2 days after ovulation from the ovary. Ovulation from the ovary usually occurs 14 days BEFORE your next menstrual period (range 12-17 days). If you have very regular menses starting every 28 days.then most likely fertile period is day 7 after start of menses (7 days before ovulation) to day 16 after menses. The problem becomes if your menses are not always that regular, the timing gets changed. To optimize pregnancy chances, having intercourse every other day (at least) starting on day 12 thru day 16 (or longer if your cycle is sometimes longer than 28 days).
While the above are general rules of thumb, ovulation prediction has become much more sophisticated. You may want to discuss these with your doctor.