Hello,
The answer can be complicated but the most common reasons would be 1)arthritis, 2)cervical stenosis, 3)muscle strain, 4) herniated disc. Always start with Xrays and then if needed, MRI. Most symptoms can be treated with chiropractic adjustments, osteopathic manipulation, massage, myofascial release, acupuncture. Conservative techniques are preferred over just taking ibuprofen or naproxen or tylenol although you can try out. Stenosis is simply narrowing in the spine canal that may pinch a nerve. Injections such trigger point injections, facet injections, epidurals, can be tried. You can try anti inflammatory creams. I developed one for this purpose. www.drjoesnutrition.com/products/all-flex-plus as it can relieve symptoms of arthritis and spasm.

Joseph C. Jimenez