Headaches only on one side of my head , and down my neck. best treatment for this?

Identify causes: Any new headache, no matter the location or patterns should be evaluated by a doctor in order to determine what the cause might be. There are many kinds of benign causes for unilateral headaches, including referred pain from jaw, teeth, sinuses, eye, neck - but you need to be certain nothing worrisome causing your problem. See a doctor who may request a headache evaluation from neurologist.