I am a similar age, male 29 and have had issues after intensive yoga retreat. Unfortunately my teachers werent the best in india. It started with a knee problem with me then spread to arms,lots of neuropathic pain, no swelling, I've had dry mouth but it is OK at the moment. Obviously you need to see a rheumatology and neurology expert. Problem is some people's bodies if they get too stressed they start messing up bad. I'm on lyrica and naproxen which help but I doubt I'll go back to pain free again. All tests are negative for me. Sorry to hear your suffering.