Heather Corinna replies:
Me and my boyfriend had unprotected sex on the second to last day of my period, we thought this would be safe as it is highly unlikely to become pregnant at that time. I am now 8 days late, and never usually late, but have been experiencing abdominal cramps for about 4 days on and off as though my period is going to start. Could I be pregnant?
Depending on when exactly you ovulate, that may not have been a safe time at all. Some women ovulate fairly early in their cycles, so for those women -- let's say someone who ovulates on day 10, and had unprotected sex on day 7 -- that would have been a very high risk time.
Please understand that there is no way of predicting what is and is not a most fertile and least fertile time for you without charting your cervical mucus and basal temperatures. The calendar method alone is relatively useless. Even when you are charting, natural family planning is NOT a reliable birth control method for younger women, and if you're going to use it at all, beyond using it properly, you'll need to use it combined with another method of birth control. For example, you might use condoms with sex for all times saving your most fertile times, and then when you are most fertile, abstain from intercourse altogether.
Given that you had a high risk, and your period is late, it's time for you to go ahead and take a pregnancy test. You can do that with a home test, or at your local sexual healthcare clinic. Too, if you and your partner have not been practicing all aspects of safer sex before this risk -- that's SIX months of monogamy and latex barrier use AND at least two full, negative STI screens for BOTH of you -- then you and he will need to be sure to get a full STI screening soon as well.
Obviously, you'll also want to sit down with your partner, too, and make clear that both your ideas about "safe" times and ways to determine what was safe were off. You'll also want to make clear that from here on out, if you do not want to/are not ready to become pregnant that a reliable method of birth control -- such as condoms -- is non-negotiable if you're going to be having sex together, okay?
And if you really are interested in finding out when your fertile times are, I'd highly recommend Toni Weschler's new book on cycles expressly for young women, Cycle Savvy.