K.D.
First of all let me recommend a book called, "Theology of the Body for Teens". You care about your gf or you wouldn't be writing. The birth control medicine has many severe side effects. It isn't normal to go w/o a period x 6 months! Yikes! Please let her know that you really do care & consider chastity as a great option.
For more information on the harmful side effects of bc visit the website called onemoresoul.com
Many of us have bought into alot of culutral lies but there are better options available to both of you.