What Causes Difficulty In Walking And Blurred Vision?

I am unable to walk for the third day. With unable to walk I mean that I usually wobble and eventually fall when I try to walk. Standing is most of the times it happens doable however I have to focus on standing. I have been experiencing this about two-three times a month since September. I once had a similar feeling in my arms as well and once my legs were too weak to stand. I sometimes have blurry vision almost like a warning it'll happen.I've been to the hospital and I checked for MS however they found nothing like MS and suggested my symptoms could be caused by stress. But I am unable to control this condition and as an exchange student it's very difficult. Please help!