People keep asking this. There are professionals who can help you with this, such as physical therapists or sports medicine specialists. If you've seen an orthopedist he or she can refer to someone who can help you with this and watch to make sure you're doing the exercises correctly to prevent further pain.
Do you have a gym instructor? did you ask him or her about your back pain?
every one who goes to gym need a couch or a instructor.
Buy these two books by Mitchell T. Yass
Overpower Pain and Pain Cure RX.
First talk to your Dr. and ask if it's OK
Have you ever tried a water work out? Water aerobics and swimming are no impact activities that are a great cardio work out while easy on injuries. Talk to your doc about that. Local y's and gyms usually have pools. Good luck