I injured my lower back a few weeks ago. It still hurts, but my doctor wants me to go back to work. Shouldn't I wait until I don't have any more pain?

Not necessarily. Doctors have found that people who have back injuries do better when they go back to normal activities as soon as possible. This is true even if the pain has not gone away completely.  

The pain of lower back injuries takes time to go away. You will need to be patient. Continue with your rehabilitation exercises, and try to do your normal activities as much as possible. Follow the guidelines given to you by your doctor and physical therapist. They can help you modify your activities so you don't re-injure your back. Let them know if a particular task aggravates your condition. They can help you find ways to change your job or change the way you do the task so that you don't hurt yourself again.