No one can figure out my symptoms, seeing a neurologist who thinks I might have Stiff person syndrome, help?

I have been getting painful spasms in my foot (sometimes both feet) for almost 2 years every time I try to walk more than 1 or 2 blocks. I have had blood work and MRIs of my spine and feet, and nothing. Pain meds don't help and the spasms don't bother me at night or when I'm sitting/laying down. My neurologist thinks I might have SPS even though I tested negative for the antibodies. He just put me on Lyrica and no idea if that will help. It has been really debilitating and depressing. I was also wondering has anyone else been diagnosed with this disease? And if so, did it start just in your feet without spreading to any other muscles at first? ANY help would be appreciated!