That sounds horrible, Rose! Prednisone does affect the blood sugars. I have had to take Prednisone at times with the problems I have and I, too, am diabetic. Since the shots are localized, it might not mess your sugars that badly. I've always taken pills...except I did have cortisone shots in my back many years ago for muscle spasms. Actually, they didn't help me one iota but this might help you.
Can a pain patch be used on your back? This might be another alternative.
They do sell large Bed Buddies that lay over your shoulders and on your back. I've seen these at Walgreen's and I also think Bed, Bath and Beyond have them too. This might give you some relief because moist heat feels wonderful with pain.
I hope you find something to give you some relief.
Sherrine