Congrats on your little girl!!! After I had my first daughter my UC never went out of remission. I had my second daughter in Jan and developed a post partum infection and had to go on antibiotics, that made my UC very angry. I don't think I would have flared if it weren't for the antibiotics.
Take care of yourself and rest as much as you can. Take probiotics and fish oil. Good luck with Immuran.