Hello and Welcome to JustAnswer. Your question is not closed until you are satisfied. I am happy to assist you with your question.
To my knowledge there is no replacement for Lamictal, and nothing for medical marijuana that has been approved for use in pregnancy. Marijuana has been proven to impact the reproductive system in both males and females, so neither of you should use it before or during pregnancy.
The only drugs that have been approved for use during pregnancy are the SSRI class of drugs such as Prozac or Zoloft. Please see a doctor so that you can find a good replacement for the bipolar drug. The SSRI should take care of the anxiety for you. I wish you the very best with your planned pregnancy.