I think you should continue with your tests.

You do not have a diagnosis yet. The word "neuropathy" is a vague term meaning "something is wrong with the nerves"....
You don't know what yet.

But I would get tested for Vitamin B12 levels and get the actual test numbers when they are available. Also request a Vit D test to see if you are low.

You don't mention what drugs you use besides the Neurontin.
Do you take cholesterol drugs?
Antibiotics recently?
Hormones?

Sometimes it takes alot of testing to get answers. When all the tests are over, and you are still stuck, that is when you need to look outside the "box".

There is a book about brain health out now by Dr. Daniel Amen.
It is called Change your Brain, and Change your Life.
It is filled with brain image data and the effects of lifestyle on brain functions. (including smoking). Many libraries have it, and that is where I obtained mine to read.