go to downloads.com and type in ovusoft fertility software. It's easy to use, and it even tells you what chance of pregnancy you have for that month on each of the days you bd and all kinds of other stuff like that. The trial is 15 days, and after that you must purchase it to continue to use it. I'd say its worth it though. There are many stories of people getting pregnant with it on the first try because it really is simple and lets you understand what's going on with your cycle.
Oh, and she's right... you really should start taking prenatal vitamins the month before you conceive. You can take a multivitamin like women's one a day (it contains 100% of the amount of folic acid you need, the vitamin that's really important in pregnancy, and it doesn't contain a lot of the "bad" vitamins that can be harmful in large amounts), or you can just go to walmart and get prenatal vitamins off the supplement aisle. You don't even need a prescription.