Take two 500mg tablets every 4-6 hours. Take them regularly. Don't wait until the pain is out of control. Some people find manipulation by a properly trained physiotherapists, osteopaths or chiropractor helpful. Learn to relax your muscles - try the Alexander Technique or Tai Chi.
Acupuncture can help muscle spasm.
People who avoid activity are frightened by the pain and worry about the future. They are afraid of hurting their backs and rest a lot waiting for the pain to get better. Copers know the pain will get better, try to carry on as normally as possible and stay positive by staying active. Avoiders suffer more and have more time off work. Copers suffer less at the time and are healthier in the long run.