Unknown muscular fatigue

   I have a hard time controlling the left side of my body, especially my
  leg, and I get muscle weakness with exercise. It started in May when I
  noticed a loss of control in my foot with my 25minute runs. It got
  progressively worse over the summer. Now I have a hard time walking around,
  I have a hard time controlling my leg and arm, and I just overall
  am weaker on the left side of my body.
   Over the course of this 6 month period I have had blood work done,
  3 EMG's, 4 MRI's of my C-spine lumbar spine and 2 of my brain, 1 cat scan,
  a spinal tap, and numerous other pokings and proddings. The doctors at first
  thought it might be compartment syndrome, then a brain tumor, then myasthenia
  gravis, and now multiple sclerosis.
   I am at my wits end. I have no idea what is going on with my body. I just
  CAN'T do things anymore. So I was wondering if anybody has ever heard of
  anything like this? If not, is it possible this could just be a virus? Is
  there any treatment for this even though the cause is unknown?
===============================================
===========================================================================
You do not say what results were obtained from your tests but I presume from the obvious frustration in your message that they were all negative.
I am interested that you mention inability to control the left side as a major symptom, as opposed to purely weakness if this manifests as clumsiness and ataxic type symptoms them I think the problem lies in the cerebellum or its connections to the rest of the nervous system. a virus is not likely since a virus would noy selectively pick one side of the body leaving the other side unaffected.
The problem causing this must be above your neck  possibly in the brainstem, rather than in the spinal cord  ( since the arms are affected ). Normally the best way to visualize this area would be with an MRI scan, this scan should have been done with Gadoliniun enhancement as some lesions are not seen otherwise.
Further testing might be possible in the form of  somatosensory evoked potentials which test the viability of pathways from the periphery to the level of the cerebral cortex, the can sometimes help localize rather than identify a lesion.
I do not see how this can be treated without identifting the underlying cause , apart from physical therapy to maximise the remaining potential on that side.
My recommendations therefore are to clarify with yiour physicians if they are considering the cerebellum as the site of the problem, find out if the MRI scans were done with gadolinium and review the possibility of eveoked potentials being of use in your specific case.