Take a muscle relaxer or anti-inflammatory if you have them. Ice your back for first day. I have an electronic muscle stimulator like a chiro uses that I bought on Amazon for $50 that I use constantly to get the muscles to relax. I also have an inversion table I got for $100 that stretches and loosens things up. Use a heating pad after the second day and try to do some stretching too. Lay flat and pull knees to chest. 2-3 days and if it's not getting better go to the doc.