Temporary lower back pain relief while at work?

Help! I am in terrible pain right now at work. Out of nowhere, I have a very painful lower backache. It hurts to move, sit, stand, etc. I work retail it is slow, so I don't have to do much moving around and when I do bend down, I do so at the knees. Also, I am alone. Is there anything to do, like stretching, that will help? Also, what should I avoid to not exacerbate the problem? Any advice would be appreciated! Thanks in advance.