Conception happens several hours after the ovulation and ovulation happens about 14 days before the next regular period occurs. 2 days before and 2 days after the ovulation are considered as fertile days in the cycle. If you get your period every month on 21st or 22nd then your ovulation should happens around 7th or 8th in the month.A period between the 5th and 10th in the month can be considered a fertile period in your case. You should have intensive sexual intercourses during that period.