A woman isn't fertile every day of her cycle. A study by the National Institute of Environmental Health Sciences showed women can only get pregnant six days out of the monthly cycle - the five days leading up to ovulation and the day of ovulation itself. If you and your partner are only having sex once a week, you may be missing your ovulation window!
You may have learned in high school health class that ovulation takes place 14 days after the start of your period, but that's only for people who have a consistent 28-day cycle, says the Mayo Clinic - and not even all of those people ovulate at the same time