What Causes Persistent Pain In The Neck?

Hello, I am 21 yrs old. For a while now I have been feeling pain in my neck( upper back of the neck). The side of the neck also feels thicker than the other side of the neck. This pain never goes away, meaning when I turn my head I always feel the pain, or sometimes i feel it automatically. Along with the pain, I get weird head aces, and other body parts ace. What could it be ?