You had heptitis history. I assume, before you took prometrium, your primary doctor had given you all the necessary physical and lab examinations. Prometrium is metablized through liver and kidney. So the doctor should monitor both organs. If the blood test suggested your liver function was in normal range. It wouldn't be a problem for you to take prometrium and the doctor would give you proper dosage based on the fact that you had a liver disease. After you stopped the medication, I assume your doctor would give you another blood test for liver function re-check.
You probably need to get a test in order to find if you are a hepatitis B carrier. Because you could give the virus to your baby.
Anyway, the best way is to consult with your primary doctor. This is a place that people could give you some suggestion. Neither they are your doctors nor they could examine and treat you even they are doctors.
Good luck.