Fibromyalgia and B12, steriods

I have fibromyalgia and I feel like a trainwreck on most days. Even a hug can hurt. I've tried various pain medications but I have found one thing that gives me a little hope. My mother told me about B12 shots. I went to the doctor, drug myself in, I literally felt like crap. He told me that along with the B12 he was going to give me some type of steroid...I'm not sure what it was called I couldn't pronounce it if I tried but I think it started with a D. Almost immediately after I left the docs office I felt a lot lighter on my feet, and just felt absolutely better, all around. The effects lasted for about 3 weeks, and gradually wore off. I'm pretty sure the steroid was what caused the difference though. One time I went to the doctor and just got the B12 shot, and I didn't feel any different. I called him the next day and asked for the other shot. My doctor told me that the medicine was in the steroid family, and it was safe for me.