Suggest Treatment For Muscle Spasms And Back Pain

help! i am in terrible pain with my back. it feels like my spine has locked and yesterday I had terrible muscle spasms. the spasms have eased and i am now just left with terrible back pain in the middle/lower part of my back when I move. I am due to start a new job tomorrow and am desperate to get this fixed! will stretching exercises or anything else quickly help it 'unlock'? Thanks