Birth control pills that are past their expiration date will still be effective at preventing pregnancy, but the chance of becoming pregnant will increase as the pills become older. It would be better to throw those pills out and obtain a new birth control pack or abstain from sexual intercourse if this is not an option.
Though you are left withonly expired pills, you should not take them because
1. They will not have the desired effect and so may end up in pregnancy
2. May have some side effects because they are already expired. 3. The manufacturer's warranty will notbe valid on expired pills.
You could take them as a back up precautionary, but any medication that is expired will probably not have the desired results, so in the mean time you should definitely be using a back up form of birth control, until you can get on a steady regiment.
As the birth control pills are passed their expiry date it cannot be medically ensured that they still contain effective inredients. Although there is a slight chance they may be ok to use, I would encourage you to seek new contraceptive pills in order to ensure efficacy and peace of mind.