I have a small lump about the size of a marble on the left side of the back of my neck by my spinal cord. Tender.?

See below. This problem mandates a real-time (face-to-face) meeting with a doctor. A history has to be taken along with a examination as well as labs and other tests. Only after all this will his doctor be in a position to tell him what's wrong and what needs to be done to help him.