Brief Answer:
A number of causes

Detailed Answer:
Dear Ma'am, I have gone through your question and I understand your concerns but this can be caused by many reasons including:
diabetes as elevated blood glucose levels tend to cause nerve damage
hypothyroidism due to fluid retention excreting pressure on peripheral nerves
kidney sufficiency as toxins build up in the body and cause nerve damage
increased alcohol intake or exposure to an overdose of besticides
bacterial infections such as Lyme disease
viral infections as EBV, herpes zoster or shingles
autoimmune diseases as rheumatoid arthritis or lupus
vitamin difficiencies including vitamin E, B1, B6 and B12
other causes include nerve injury and pressure excerted by soft tissues or bones
However , the treatement basically is based on treating the cause of the nerve damage but analgesics as ibuprofen for mild pain and narcotics for more severe pain.. in some causes percutanous nerve stimulation can be used when the cause cannot be treated to stop the nerve from passing pain stimuli.. I hope you find this helpful

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