Though it could be related to something else, you're probably suffering from drop foot—also called foot drop, confusingly enough, by some medical authorities.
Drop foot occurs when you are unable to lift the front part of your foot; you end up dragging your toes when you walk. However, keep in mind that drop foot is not a disease—it is the result of an underlying condition. It can be caused by various nerve, muscle, or brain injuries. Since your symptoms developed after childbirth, your case is probably related to your nerves.
The nerve that drop foot is most associated with is the peroneal nerve, which wraps from the back of the knee to the front of the shin. It is very easy for this nerve to become damaged or compressed during natural childbirth. Women find their peroneal nerve damaged from pushing down so hard when their legs are in the crouched/frog-like position when they are trying to give birth.
Once you notice any numbness or tingling in your feet, you should contact your podiatrist right away. As with many conditions, early detection and treatment are key to a full recovery. Depending on how severe your drop foot is, your doctor may have you wear lightweight braces or orthotics for a while. Physical therapy is also common, but surgery may still be necessary to repair a damaged nerve.