I have a bulge in lower abdomen that is soft when pushed and appears when I do a sit up or make that kind of motion. No pain. What is this?

Hernia. This certainly sounds like a ventral hernia: a separation of the abdominal muscles. permitting a bulging of the covering of the intestinal contents: mostly benign if not causing pain and quite common after abdominal surgery and or with excessive weight, obesity or weight gain.