What Causes Severe Pain In Lower Back Radiating To Butt Cheek And Legs?

Hi, I had fallen down the steps 2 days ago and landed on my back and tailbone, and 5 years ago I had back surgery with a fusion, with screws. I did however go to the hospital to make sure I did not break anything, but I am in alot of pain and it goes down my left butt check and down the back of my leg, and sometimes feels like I am about to fall, due to the weight is to much. I am up at 2 a.m. because the pain is overwhelming, and I am starting to shake as well. When I went to the hospital they said nothing was broken which I thought was great, but am concerned about the fact that it hurts when I walk, when I go to get up from toilet, chair, ect...'

Should I be concerned about this? Or just let it run its course?