I honestly don't know whether acupuncture will help you. It may temporarily relieve the pain but if you have spinal structure problems and your back keeps "going out" it sounds as if your spine may possibly be slightly out of alignment. When this happens, over a period of time it puts pressure on the other ligaments and something eventualy has to give.
I can recommend trying a chiropractor. A good one will x-ray your spine to check this and you may well find that a few simple manipulations will straighten things up to prevent this happening again in the future. It will probably cost about �40 for x-rays and about �30 for a manipulative session. They should also be able to suggest certain exercises to do regularly to try and prevent the problem happening again.