When you were talking to your doctor about exercises you could do, did you talk about yoga ?
Yoga has several good poses that can help a person who has back issues or sciatica. However, you should take a class with a good instructor if you've never taken yoga. Some poses can help. Others can hurt. It depends on how your body adjusts to the pose.
This is an example of poses that might help relieve any lower back or sciatica you may have. www.fitsugar.com/Yoga-Sciatica-23949884
In general, when it comes to back issues, a person really should consult their doctor. Will your doctor take your calls even if you don't have insurance ? Most will try to answer any questions you have especially if you have been a patient before.