Didn't do a damn thing for me.
As we speak I am flat on my back, killed it Sunday working around the house.
Went and saw the Chiro and massage last night, still locked up and can't walk.
This crap sux.
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I have the exact same problem stemming from a back injury from the military. Honestly stretching is not the answer until the pain is gone. I know that this sounds a little counter intuitive, but if you stretch injured muscles or tendons it just makes the healing time take longer and it will be apparent when it hurts worse after you stretch it.
What you need to do is stay off of it and maintain the best posture that you can. Do not do anything to agitate it for about 1 - 2 weeks until the pain is completely gone. Then start stretching and continue to take it easy. The most important thing is that you correct the source of the problem or it will just keep coming back. That was the hardest part for my stubborn ass. Chances are the lumbar support that your chairs at work or in your car supply is inadequate. There is a natural S-curve that the spine is supposed to make and if your slouching while sitting or standing with bad posture, your spine will put pressure on itself unevenly causing areas of high stress that result in even small activities causing incapacitating pain.
I have bought some little pillows to push out my lower back while I am driving my car and I forked out the extra cash for nice office chairs at work and at home so that I minimize the time that I slouch over. Then from there it is just a matter of keeping your back flexible and stretched out as often as possible. The last time I had a severe back sprain / spasm I literally could not go from a sitting or laying position to a standing position for two days. It was just like you said too hurting to breathe, and that was just from playing a little football with my brother one Sunday.
One more thing, there is a chance that you have an acute back injury so seeing a doctor is a good idea. If you continue to just accept the pain as it comes along, over time you will develop other problems like the ones that others have listed here. Ensuring that you have correct posture and flexibility will not only stop the pain but it will help to prevent further injury.
Having severe back pain for so long I have tried everything, physical therapy, acupuncture, chiropractors, voodoo (not really) - none of it helps and much of it makes it worse (the chiropractors really put me in a bad way). I can get surgery for mine but it's a 50% chance or better that I will be in a wheelchair after, so I have to just manage my pain and move on.
That being said, I HAVE been to doctors and you should too.