"Way too many tacos at lunch," she captioned a video that showcased her growing belly. "Seriously though, as scared as I am to have three under three, I'm so grateful God picked me to be the mommy to my kids and we can't wait for number four to get here!"
Maynard added, "My little tribe can't wait to meet their new brother or sister (it's a surprise!) in the next couple of weeks!"
Maynard, who wed Johnson in June 2014, is already mom to 12-year-old daughter Ricki (whose father is late race car driver Ricky Hendrick), and sons 2-year-old Jennings and 11-month old Gibson.
ET caught up with the blonde beauty last December, when she opened up about giving birth to her sons so close together.
"The third [child] has been the hardest adjustment, I would have to say," she shared. "They're 14 months apart. Jennings took his first consecutive 10 steps in the hospital right after I had Gibson. The day I went to the hospital, he starts walking. I'm like, 'No! Please no! I'm not ready!'"
ET has reached out to Maynard for comment. See more on her busy life after The Bachelorette in the video below.