http://www.mult-sclerosis.org/diagnosingms.html
This is a great site that will fully detail the diagnostic steps for MS. (above link)
Usual tests are: a lumbar puncture with oligolconal bands and no indication of infection in blood, blood work that rules out all symptoms, MRI of brain and possibly neck and back that shows white matter lesions, a neuro exam with indicative responses and reflexes (L'hermittes sign, Babinski's response).
You may want to see an MS specialist. Call your local MS society for a list of doctors.