Is It Safe To Use Cortisone Injection To Treat Pinch Nerve And Lower Back Pain?

I had spinal fusion surgery October 15, 2014. I had spinal stenosis L 5, S 1. Before the surgery I had leg weakness and shaking. When I would stand to much I would get leg cramps and cramps in my feet by my toes. After my surgery my feet went numb and hips hurt when I woke up in hospital recovery. I had leg spasms really bad. The leg spasms went away but I still have numbness in my feet and legs. My right ankle is numb and weak. When I stand my legs are weak then I start to shake and my lower back starts to ache. I had a bunch of test done. I can t get any answers to my problem. My surgent doesn t think it from my surgery. But I think it is. I had mri of my head my neck my mid back and finally of my lower back. I had an E.M.G. of my legs and it said I had a pinch nerve in L 5. The doctor still doesn t think it from the surgery. Could a pinch nerve cause weakness and numbness and shaking.Would a cortisone injection help me. I just want to feel better. Thank you