It's not that difficult to get pregnant at 47 -- as long as you have two things: someone else's eggs and at least $25,000 to $30,000 or so. ;)
It's highly unusual for a woman to get pregnant on her own after age 45. According to the Centers for Disease Control and Prevention, in 2008 there were 0.7 births per 1,000 women ages 45 to 49, compared with 9.9 births per 1,000 women ages 44 to 40.
Even though you are still having periods, ovarian function waxes and wanes. While you still have periods, you will have some anovulatory cycles.
Although it is statistically unlikely that you would conceive at your age, it is theoretically possible. Calculating your "fertile days" is not really possible given all the variables. You could use an at home ovulation kit to verify you are not ovulating prior to intercourse.
My understanding, from reading several of your posts, is this is not a regular partner. I personally would use a condom. That would protect you from the very remote possibility of pregnancy as well as protect you from STDs.