and movement?

  Can someone help me out?
  I have been having a bit of pain in the past year, and it's getting worse.
  When I was jogging regularly, my arm/shoulder/neck would hurt so badly that
  I had to stop after a mile.  Eventually, my arm went numb and my strength in
  that arm decreased.  I stopped jogging, but my arm still hurts occassionally.
  The other day I went on a walk and it hurt afterwards as did my neck.  
  By the way, I'm an otherwise healthy 20 year old.
  My arm hurts (dull pain) all the time now.
  I had an MRI (c-spine) and x-ray (also C-spine) that turned out normal.
  So basically no one knows what is wrong with me, but I'm really worried about it--
  I'm even having bad dreams.
  Please help me!
=
If you were 35 or older, I'd say pretty quickly that this sounds like a cervical radiculopathy - compression of one or more of the nerve roots coming from the spinal cord out the neural foramina past the bony structures of the spine. The reason I quote the age is that wear and tear changes (degenerative spine disease) is more common as you get older. No magic number, but 20 is a bit on the young side.
However, you don't just need to have shriveled up or herniated discs making your life hard. Some individuals have other structural abnormalities (a big ball of blood vessels, or a tumor, or other sorts of malformations).
A cervical spine plain X-ray will not cut it. An MRI would show any of the structural abnormalities mentioned (including disc disease).
If the study is normal, it at least rules out threatening lesions. But it doesn't prove or disprove pain or other symptoms. It is not uncommon for people to experience a significant amount of pain or numbness with minimal changes on MRI - that is, minimal or no structural damage. This is good in that permanent damage to neural structures is not likely, but often frustrating for patients who wonder if their doctor takes them seriously.
The most important thing, before any highfalutin tests, is a careful evaluation by the appropriate specialist. I vote for a neurologist - you are welcome to get a first or second opinion at CCF - call 800 223-2273, ask for 4-5559.
As you know, this information is provided for your medical education. Specific comments regarding diagnosis, prognosis, or treatment options must come from your doctor after appropriate evaluation. I hope this helps. CCF MD mdf.