One of the most definitive guides to birth control is called "Taking Charge of Your Fertility" by Toni Weschler. I have done so much research online and otherwise, and have found this book to be extremely helpful. Of course, there are others out there (and I own a few), I would recommend researching ALL of them. You can never have too much information.
As far as the chemicals and affects of birth control: every pill is different, BUT they all have significant dangers to the woman's body. Severe side effects have been documented for everything from migraines, to ovarian cysts, an increased risk of ALL types of cancer, and even cardiovascular difficulties (increased risk of heart attack, etc). Many women are not aware of these dangers/risks, and do not experience any side effects...but KNOW what the dangers are, and there are proven SUCCESSFUL alternatives.
Birth control pills alter many systems in the body, and each have a different method. Check out the following site for some general pros/cons and basic information about the different kinds of contraceptives: http://www.4woman.gov/faq/birthcont.htm
This is a good starting place to discover information about many different kinds of birth control (and the pill).
Also, for an excellent explanation of birth control pills specifically, check out: http://kidshealth.org/teen/sexual_health/contraception/contraception_birth.html
And finally, every woman's body is different, and thus...even with all the research in the world, you may find your body reacts differently to the "pill" than other documented sources.