The only thing I can think of offhand is that too much glutamine, could push you into too much glutamate synthesis.

Alot of glutamine is absorbed in the GI tract lining... so excess in the beginning would not be so obvious. But then once that is saturated, that glutamine would go down the pathway to
glutamate, which can be problematic when too high.

This is the biochemical genetic pathway for glutamine:
http://www.genome.jp/kegg/pathway/map/map00471.html

And this is a diagram of a synapse where glutamate is the neurotransmitter:
http://www.genome.jp/kegg-bin/show_pathway?hsa04724

One has to look at the maps for a while, to finally realize how complex the biochemical reactions really are. They typically HUMBLE me... sort of the same way looking at the stars does but only in reverse, since the Kegg pathways are internal, and not out there in infinite space!

But there is a hint, in the second link: Glutamate is involved with calcium signaling. When calcium is excessive it does cause numbness on the face...around the mouth as one effect. Your numbness may be similar.

One intervention you can try is to make sure you are getting enough magnesium either in your diet or supplemented. There is a new lotion, Morton's Epsom lotion that is really good, and you can target the foot better with it than oral. It is available at most WalMart's now for a very low price. (also on Amazon for a bit more)

http://www.mortonsalt.com/for-your-h...-epsom-lotion/

This is the Wiki on glutamate receptors:
http://en.wikipedia.org/wiki/Glutamate_receptor
Pages like this typically need more than one read.... because it is so complex, I always read them over and over (with time inbetween to let it all sink in).

Try the Morton's on the top of the foot, and along the side. The skin is rather too thick for bottom application.
Cutting back on your glutamine, avoiding MSG in foods, and trying the magnesium, may reveal a change for you.
Magnesium is a NMDA receptor antagonist, and blocks excess glutamate excitation.