Hi ~ It sounds to me like you certainly don't need Cymbalta. While it's true that it does have "some" pain properties in it, it is NOT primarily intended for pain relief. It's major intent is for depression! That's probably why you gained weight.
Have you had an MRI? If not, you need one with and without contrast material. It sounds to me like this could be spinal related, possibly a disc problem. Your symptoms are like mine, and I have sciatica. I've had it for 24 years, and it's awful! Mine is caused by the spine (discs) and I have to take pain medication along with other meds for the burning & tingling and stinging. I'd suggest asking your doc for an MRI if you haven't had one. If you HAVE had one but it's been over a year, you need another one to see what's going on.
Best of luck and I hope you can get some answers. Please let us know what you find out. God bless. hugs, Lee