I also had test come back clear for rheumatoid arthritis, lupus, and hepatitis
After talking to my psychiatrist they put me on Gabapentin, for my bipolar, anxiety and pain. It has helped fairly well so far, but I still have a little anxiety, and pain sometimes. It hasn't been a super wonder drug, or a cure by any means, but so far it has alleviated my symptoms by 50-75%. I have only been on it three days now.
I am very sorry about your pain, and I hope you get it figured out soon.