If you'd like to know more about Cymbalta from people that are actually taking it you might try the Cymbalta group at Yahoo:
http://groups.yahoo.com/group/cymbalta
I moderate the Celexa and Lexapro groups there. The two largest, main, ones. I joined the Cymbalta group because my doc was thinking about putting me on Cymbalta at one point. What I've see so far is there is doesn't seem to an in between. It either works fairly well for you or it doesn't. Period. The 'doesn't' part includes intolerable side effects.
Cymbalta is widely used for all kinds of pain now. PN among them. I think some of the sides depends on the dose. *If* you experience sides that is. There are a number of people that have none at all after the first two weeks.
Look at it this way, if it's not helping in 2 or 3 weeks you can always try something else.
I'm sorry you're having trouble sleeping. That's when my pain is always the worst. I'm one of those people that cannot tolerate sleep deprivation at *any* level.