It can take about 2 years for your internal organs to go back to normal after a pregnancy, so don't get discouraged! There is no such thing as losing your shape forever, lol! I know it sounds discouraging to get back into shape right before planning another pregnancy - but it will make the next "getting into shape" time easier then if you just let things go.
I'd suggest doing some core exercises along with cardio to burn the fat. It will come. It takes a while to retrain those stretched out ab muscles, but they can do it. Once they get stronger, they'll burn off more of the fat and the skin will go back in time as well.