My husband and I have used natural family planning in order to get pregnant. After trying for over a year, we got pregnant after only three months of practicing NFP.
There is a lot more involved than just being told that from day 1-7=infertile, 8-19=fertile and 20-32=infertile. It doesn't really work that way for most. Women are really only 'fertile' for approximately 24 hours. There are several resources you can find online to help you learn more about the process of Natural Family Planning. There is also a course you can take from the Couple to Couple League International. It is a Catholic organization and they offer courses all over the country and also have a correspondence course that you can take. There is a cost, but if you are financially unable to pay, they will still give you the course to take at home. It is very interesting stuff. I am not Catholic, so I don't necessarily agree with everything they say (though I'm not sure, I didn't read the entire book). So, what I did was just take the nuts and bolts of information and use that. Like, it doesn't matter what religion you are, a woman is still going to have a period and ovulate (unless there is something medically wrong, of course). The course teaches you how to chart your fertility and read the results of the charts in order to avoid or achieve pregnancy.
No method of birth control is 100% though, so this definitely isn't the 'golden ticket' to not getting pregnant. It's still a great resource though. What better way to achieve (if possible) what we want than to know how our bodies work. :)
I hope you find what you need. If you want more info on charting and what it's all about, let me know.
God bless,
A.