i would focus my mind on the baby. would you really be able to destroy his life, just because you ''couldnt'' stay away from the stuff for 9 months?
the truth is, it would be YOUR fault if there were somethiung wrong with the baby.
talk to your doctor, there are people who can help you with it, its going to sound rude but you need to keep yourself together for those 9 months, so that youll have a healthy, precious baby, and stay away from the meds too
and realize, that you have to grow up now, be a responsable adult, who is in charge of another precious life, and do all in your power to assure him a healthy start.