Having neuropathy pain and wanting [VERY MUCH!] to be diagnosed goes with the territory. Thing is, that Neuropathies and other neurological and even other outside medical conditions overlap, seem similar, and mimic each other...so testing is a long and convoluted route.

First please, check out NeuroTalk's Peripheral Neuropathy forum:
http://neurotalk.psychcentral.com/forum20.html [Click on the blue and you'll be there!]

Next read the 'stickies': 'Important Links/Stickies', meaning that there is a lot of info [Info that's worth keeping] there that can help you...

This web site is useful about what the basic neuro diagnostic process is...what these docs look for at initial exams and why they test 'this' or 'that'.
http://www.neuroexam.com/content.php?p=2 A good deal of diagnosing is to 'eliminate' the things that can be tested for.
Next is a detail on diagnosing peripheral neuropathies:
http://www.aafp.org/afp/980215ap/poncelet.html
Finally, and I can't make it more clear? Along the way, get copies of all your test results! This can make it easier in the long run if you want to get a second or third opinion from other docs/specialists in the future.
A good PN resource to help you keep track of your tests [you mite not need all of them, but at least you will know where you stand in the 'testing-go-rounds] is www.lizajane.org [which is down rite now, but will be up soon I'm sure] and this site as well-tho a lot technical: http://neuromuscular.wustl.edu/lab/nvworkup.htm#lab

This all IS a lot to read and asorb, but it will help you track where you are in all the testing.

As for 'how long' it takes? For some folks years! For others just a few months. It varies from person-to-person just as does the pains.
It does sound as if your docs are trying very hard to do all the key tests as they get many other problems [such as Lyme's] crossed of the possible list.
I sure hope this helps! See you around soon! - j