Your symptoms may be caused not by a abdominal disease but by a backbone disease. If there is a spinal cord
constriction pain appears, and its localization is dependent of the sick backbone region. This pain is often associated with headache and hands/legs numbness
. So a MRI of a backbone might be advisable as all others tests showed nothing.
Another disease that gives joints and abdomen pain is Crohn`s disease or other immune dependent intestines disease. According to all tests you have mentioned, there is no small intestine
examination. That is why CT Enteroclysis might be necessary to rule out any small intestine disease.
In ruling out other, rare disease there should be Hepatitis A
included. To rule it out liver enzymes and porfine metabolites in blood and urine should be tested.
Hope this will help