You should have a formal evaluation with a neurologist who can assess the muscle and nerve function in your leg. Possible causes for your pain do include musculoskeletal problems (which you have been evaluated for), but also include peripheral nerve disorders. You have stated that you had a nerve conduction test, but did not provide the result (I assume it was normal). Depending on how the test was performed, very focal nerve problems can be missed. Also, this may represent a small fiber neuropathy, which would not show up on standard nerve conductions.
Therefore, the evaluation by a neurologist would attempt to discern if a particular neurologic problem is present. Good luck.
I had severe bilateral plantar fasciitis.Nothing helped.I couldn't walk ,not just in the mornings when getting out of bed.I found that taking FOSAMAX(Alendronate)70mg once a week for 4 weeks worked wonders! You may have to try it for 2 or 3 months.It must be taken in the morning on an empty stomach with a full glass of water and you must remain upright for 1/2 hr afterwards and only eat after 1/2 hr.Fosamax is a bisphosphonate-a drug used in the treatment of osteoporosis .I am in the medical profession,so I knew and tried all the other treatments there are except for surgery which I wasn't prepared to undergo.By the way ,let your doctor check you for reactive arthritis or spondyloarthropathy which can sometimes cause plantar fasciitis.