Have you been under any stress recently. When I was 19 I'd just come back home from summer exams and my neck went that bad that I could barely move it and it kept shaking it was the most painful thing I've ever had I had to use walking sticks for stuff like getting in and out of chairs and out the bath and shower.
Anyway the doctor said it was stress induced exams must have upset me alot more than I thought and gave me antiinflammatories, strong painkillers and a sheet of gentle head exercises that I had to do every day. Moving my head gently up and down side to side that kind of thing so it might be worth trying to do gentle head movements every hour or so.
Anyway hope it gets better soon