I have had a steady headache, severe at times for two months, spontaneous lactation, left arm weakness and double vision, weight loss, no tumor on ct?

Consider MRI: There may be a tumor in the pituitary gland area that was not seen by the ct scan i would talk to your md about that possibility.

Tough to know: Would want to actually see the imaging of the brain, see blood work, get a full history, and have a chance to examine you prior to making serious guesses about a diagnosis. This is were you might want a second opinion from an internist to get to the bottom of this. Could be related symptoms or could be several problems together.