I cannot give you any definite diagnosis over the internet
If your MRIs have been
normalNormal saline flush, then any structural lesion of the spine ie discs, lumbar stenosis is unlikely.
Pain that radiates from the back around to the stomach, that followed the distribution of the sensory nerve in that region, can be caused by a herpetic infection, even in the absence of the classic herpetic rash (shingles)
Pain medication that targets nerve pain (ie neurontin, pregabalin), may then be more effective than other pain meds
(There is no role for treatment of the infection unless started in the first 2 weeks of the symptoms.
I am not sure what the heat sensation in your thigh is - there is a nerve that supplies the skin there that commonly gets compressed or pinched ('meralgia paresthetica')
Other chronic pain options such as nerve stimulators, rhizotomy etc (cutting the sensory nerve) can be explored with a specialist at the Cleveland Clinic Pain Center, a national center of excellence for the treatment of chronic pain.