The Cougar Town star and her husband Jason Packham welcomed son Dashel five years ago, but she wasn't able to enjoy the bliss of being a first-time mum since she was struggling with her own demons.
Opening up about her troubles as a new mum, she tells UsMagazine.com, "I would flip through celeb magazines... and I just couldn't get how these mums, like Jessica Alba, lost so much weight so quickly - and yet I couldn't... I felt broken. I felt like an outsider in my own community. There just are not a lot of overweight people in Hollywood. I felt like the jerk who couldn't figure it out."
The 42 year old finally signed on as a spokesperson for weightloss programme Jenny Craig, and she insists it's the only way she was able to get her body back.
She explains, "I had tried every other diet in the world and decided to give Jenny Craig a try. The first week, I lost five pounds and then lost an average of two pounds a week for 16 weeks. I lost 35 pounds total. It changed my life."
Sullivan has kept up with the diet plan ever since, and she attributes the firm to helping her get fit again after the arrival of her little boy Beckett, now three: "When I look back to when I had my first son, I was unhappy. I couldn't understand why the weight wasn't just falling off. I wish I could have that time back.
"With my second son, I enjoyed the whole process of him being an infant more because I wasn't mad at myself. When you are mad at yourself, you are mad at everybody. That's the problem... I may not look like (Jessica Alba), but at least I can keep up with other actresses now. I feel really good about myself."