Sweeney, 31, is pregnant with her second child, a daughter, and those who watch the new season of the NBC reality series (which starts Sept. 16) will also see her belly start to expand.
"It's really the only time in your life that you're supposed to gain weight," Sweeney told PEOPLE at Tuesday's auction of celeb-donated jeans for Clothes Off Our Back, which benefits children's charities. "They say that you're eating for two, but you have to remember that one of the two is only five ounces. It's not the same."
During her early months, gaining weight was the last thing on her mind. "I was really morning sick," she reveals. "It was brutal. I would order my favorite things from restaurants, and I would get it and say, 'Get that thing away from me.' Grilled chicken or tomatoes would be the worst. I would tell my husband to get it away from me."
Luckily there was one thing she could eat. "All I wanted was Cheerios – it was all I could eat for two months."
Satisfying Sweet ToothMorning sickness has long since passed, and Sweeney is now making the most of her cravings.
"I definitely have a sweet tooth with this pregnancy that I didn’t have with my son. With my son, I craved savory things. My doctor said to buy fruit at the farmer’s market. I bought a cantaloupe, and I had to stop myself from eating the whole thing. I cut it up and put it in this big bowl and then next thing I knew, half of it was gone," she says.
Sweeney still manages to work out, especially for what she considers her "problem" areas: "My butt, my thighs, my arms – the whole thing."
Her workouts range from hikes to her costar Bob Harper's spinning class. "I'm addicted to that – I definitely still do that while I'm pregnant," she says. "I try to make sure I don't do the same thing twice. … Everyday is different, and you can shake it up every day."