How Can Lower Back Injury With Bruising And Pain Be Treated?

Hi. I fell down the last 5stairs at my job. They are metal stairs and my left lower back landed right on the edge of one. This was at 5.30am. its now 3.20 pm and i cant sit with my back touching anything, if i bend a certain way it hurts, walking feels like there is a tight pressure and there is a bruise about 3inches long going horizontal across my back where it hit the stair. what should i do?