What Causes Pain Along The External Jugular Vein?

I have had pain centered along my right outer jugular for about two days now. It doesn t hurt unless pressure is applied, or I turn my head the wrong way. The pain seems to be centered at the point where my neck meets my jaw line, but follows the vein about 2/3 of the way down my neck and extends about 1 inch into the surrounding muscle. The tenderness to touch increases as I apply pressure closer to the vein. I will be 27 by the end of the month, I smoke, and my mother has Hashimotos thyroiditis, no real health issues.