It took your body nine months to build itself up for the baby, and it will take time to return to your "normal" self, though the size may always be slightly altered.
The first few days you may notice that your area very warm all the time, perhaps even sweating profusely. This is generally due to hormonal changes and its helping your body to rid itself of the fluids that have built up to sustain the baby and the placenta. This is generally not painful, just annoying.
After pains are the contractions that help your uterus return to it's normal size. The begin after the birth of the baby and are normal and natural, bringing the placenta out. For nursing moms, the oxytocin released while nursing may cause you to notice some cramping right after the birth and during the first few days of nursing. This is a good sign that your body is working. If you have trouble expelling the placenta or are bleeding too much, try nursing the baby, if that doesn't work uterine massage will usually be initiated, and then a medication will be given to help you contract to prevent bleeding if all else fails.
See also: Postpartum Pain Relief