The best thing you can do is to improve your diet by adding more fiber. Eat extra servings of vegetables and fruit, and whole grain cereals like oatmeal or granola. Try eating dried fruits, especially prunes. Juices may help too, but be aware that fruit juices contain a lot more sugar than you may wish. If you are still eating white bread, changing to a whole grain variety is a tasty way to get fiber as well as essential vitamins.
Do not use laxatives, enemas, or stool-softeners without consulting your care-provider! Sometimes these can cause labor to begin prematurely.