Sounds like you two need to up your birth control. You can use spermicide with the condoms, she can take birth control pills and you can use condoms. There are cervical caps to use with spermicide and condoms.
Go to planned parenthood and discuss with them birth control options. Most are low cost and even free. They also conduct classes for teens/young adults to teach them how to use condoms and what methods of birth control would be best for them.