Well, Nutrasweet is one to avoid. The aspartic acid in it can be neuroexcitatory.

Also make sure you are getting enough magnesium. Low magnesium also leads to excitation of the NMDA receptors.

Check your D3 levels and see if you are really low. We had a fellow on PN 2 years ago who fixed his low D and his pain went away!

If you receive vaccines regularly like flu vaccine every year, I would certainly eliminate eggs. There are egg peptide fragments in egg derived vaccines.

I think the best elimination diet information I've seen yet is in this book:
Obesity's answer:
http://obesitysanswer.com/
The last 1/2 of this book goes into detail about removing allergens from your food. This is how I discovered potatoes were so bad for me.

Some people are highly allergic to citrus fruits, too.

But also look at things like dry cleaning. You may bring those solvents into your home and against your skin.
Out gassing of formaldehyde (common in new homes).
Black mold in damp places

You will want to try the oral methylcobalamin instead of B12 shots. Take 5mg daily on an EMPTY stomach for 3 months. Your blood levels should come up quite a bit. If you have copies of your tests, see what your B12 really was. Methyl B12 is the active form. Cyano in most shots is synthetic and some people don't respond to it. Methyl B12is not expensive, and most commonly online. iherb.com and Puritan's Pride now have it very low price.

It would help me if you listed your supplements so I can guide you more accurately.