Hi grinnin, I don't know anyone who became vegetarian or vegan because of chronic pain, but I do know a couple of vegetarians who complain of chronic pain so my conclusion is that simply being a vegetarian doesn't eliminate all pain.
I don't know if this thought will help or not, but I will offer it just in case. I do know a few people who had chronic pain who achieved great relief just by drinking more water. Not tea or coffee, just natural filtered rainwater. I think too many people overlook the importance of allowing their body to naturally flush toxins and other things that build up and cause restrictions in their blood, cells and organs.