Dewcole, Back pain can be very common in people with MG. When muscles get weak, it can throw off the spine. You have to be very careful when doing anything invasive with the spine. I'm rather opinionated on this since I knew of someone who ended up having a botched one and being in a wheelchair the rest of his life.
Did you and your doctor figure out why you're having back pain?!

Sometimes physical therapy can do wonders. I've had it in the past and they do much more than massage. They can do ultrasound therapy plus give you tips on strengthening your core muscles to keep your back in good shape.
If you had the epidural done, I hope it went well. If you keep having pain, consider a 2nd opinion from a neurologist and/or a referral to PT.
Annie