Pregnant and Getting Hitched

My fiancé and I used all of 2014 to plan our wedding in May of 2015. Last Christmas we were blessed to learn we will be expecting out first little person in August 2015. After finding this out, we scrapped our original plans and went with a smaller ceremony 4 weeks from now. I bought my dress a little over a year ago (which is way too big, a sale that worked in my favor) which is a sweetheart mermaid dress. But! What kind of undergarments would anyone suggest for a 17 week bride?