What Causes Weakness And Tremors In The Hands And Legs?

my symptoms started with balance problems, weakness in arms and feet, tremors in hands and legs, double vision, forgetfulness. I ve been to an ear doctor, an eye doctor, and a neurologist t. I ve had a MRI of the brain, which showed nothing, and a nerve conduction test on my legs. that also was negative . all blood tests have been good. now, six months have passed and nothing has changed. any ideas would be great.