If you're not already taking high doses of anti-inflammatories, start now. Ibuprophin 800mg three times a day is the most you should take. That can be harsh on your stomach, tthough. Nabumetone is an alternative that's easier on the stomach, and only requires 1000-1500mg per day. Valium is also an effective muscle relaxer. Ice for 10min at a time (no longer or your body starts to reheat, reversing the icing). Do this every other hour.
Best advice: get an MRI if you have insurance or can afford it out of pocket. Ask for an MRI with contrast (they inject a dye into your veins that helps diagnose scar versus healthy tissue). If it's something worse, that'll tell you, and I would get on that ASAP. MRI's typically schedule a week or two out, but a doctor can get you a rush/priority scheduling if he judges it to be urgent.
I would hate for a chiropractor to tweak something if it turns out to be more serious than what you think it is.
FWIW I have a lot of experience with nerve pain and MRI's. In fact, I'm getting another one this Saturday (my 5th or 6th). See your primary care physician or go to urgent care (it should be the same co-pay, and isn't super expensive like an ER visit like some people assume).
Until you get imaging done, do what I mentioned above and only use that arm if you absolutely have to. That shoulder surgery may not have healed properly, either, so get some imaging done, and have a neurologiest or orthopedic specialist take a look at it.