hi jen
Because your period varies slightly in length, the ovulation calendar has probably worked out your most fertile "window" bearing in mind that it doesnt know exactly when you could ovulate, and also the fact that you are considered fertile for up to 5 days before ovulation as thats how long sperm can live for in the right conditions.Most ovulation calendars include these potentially fertile days before ovulation aswell. So i would take the advice of the calender and BD every day, or at least every other day within that time window they've given you, or until you know or think you have ovulated.
As for the pains you've mentioned, im not sure if they're ovulation pains or not. Are you monitoring your CM (cervical mucus) or using OPK's? Both of these can help with determining when you are ovulating, as can charting your temperature, which will confirm that ovulation has occured.
Good luck, and baby dust!!