What Causes Recurring Stiffness In Muscles,heaviness In Waist And Weakness In Leg?

Hello Doctor,I am from Ranchi basically but staying in Pune since last 7 years. Since last few years i have been suffering with some recurrent problem.I will explain you about my problem first. It happened in 2006 first, when I was unable to walk. It was due to heaviness in my waste and weakness in my legs and whole body was suffering with tremors. The same thing got repeated in year 2008. This time it was more severe in terms of tremors, muscles stiffness but again more visible in Lower limb. Both the time TSH was dis-balanced and diagnosed as Hypothyroidism. But they never gave me medicines for that. Along with that in 2008 B12 deficiency also got diagnosed. Now again the same episode got repeated in month of February 2010. This time TSH was normal and B12 level was also normal. TSH was normal before that also whenever i got it tested after every 3 or 6 months. Doctor has done LP, MRI Cervical Spine and Homocysteine. All the reports are normal.please suggest.Regards,Preeti