Hi leimommy,
Don't stress yourself out. Stay calm. Just explain to your elder one that u are going to give birth to his/her baby bro/ sister. Bought the toddler a toy that tell him that it was a gift from the baby. And start practicing to let the toddler sleep by him/herself. Tell the toddler that he must be brave & strong becos he is going to be a big brother.
Jia you!