You might want to view the list of causes at this site
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001884/ In the introduction it mentions over 50% of cases have no known cause.
That said, do you have any gastrointestinal symptoms? Diarrhea, constipation, bloating, pain, heartburn? If so, the one test they did not do looking for inflammatory bowel disease in the capsule endoscopy. It looks at the 21-23' of small bowel that the upper endoscopy and colonoscopy can't reach. If you don't have GI symptoms, then it is probable that you fall into the 50% unknown or one caused by other inflammatory diseases or infection.
Have you tried a NSAID to help reduce pain and inflammation? I do know that prednisone helped clear mine the fastest. Sorry you are having to cope with these.