Horners Syndrome

I'm a 31 year old male, two weeks ago after running I noticed the that I was only sweating one the left side of the face along with pale white skin on the left side.  Since then I have went to my doctor and he thought this was possible horners syndrome.  I do not have any signs of droppy eye or different size pupils.  I've had chest x-rays, neck CT with contrast, and a brain MRI that were all negative.  My doctor still believes it is Horners Syndrome and I have an appointment with a Neurologist in a  month.  Any time I'm outside and begin to sweat I do not sweat from the left side, the flushing of the face only happens during a long work out.  Yesterday though I ate some salsa and this did produce sweat on the left side of my forehead.  Are there different nerves involved that would cause this to happen?