I had my baby 9 months ago and still have back pain. I've never had back pain until the epidural. I don't understand?

Common concern! Your concern is common and often occurs after pregnancy. The key is conditioning after delivery. If you do not respond to exercises then you may need to see a provider to assess the cause of pain. Mri scan may be needed to make certain that you do not have an injury related to the pregnancy.
Pregnancy related. My guess would be that you have mechanical back pain from the strain of carrying a baby and the labor process. The normal curve a the lumbar spine is greatly exagerated the bigger you baby grows in you. Your center of gravity, gait, sleep position has all been different during this time. I am an osteopathic physician and treat many women pre and post delivery to rebalance their spine and pelvis.
Pinched Nerve. Sounds like you have a pinched nerve in your back. I would suggest seeing a pain/spine specialist to evaluate you further to evaluate what level and what can be done to treat you. There are interventional treatments besides medications and surgeries that might reduce or eliminate the pain altogether.