Have similar problem, got some relief by changing pillow to small grain pillow which tuckes into neck & lets head hang lower. Seems important to keep neck vertebrae under bit of tension rather than compression. Saw osteopath & massages but not much help, going to try chinese massage next. I'm 56.
Sleeping habits / Sleeping Conditions change in this 2 week time period of on-set?
Could be something Serious, however, would not take it lightly.
Ice your neck , take an anti inflammatory such as motrin, as well as pain lotions like aspercreme, capzasin etc. Is it possible that you are sleeping in a funny position? Maybe your pillow isn't soft enough or maybe it's too hard? Is it possible you over stretched it and Maybe you pulled a muscle? A pinched nerve maybe?
Getting checked for meningitis isn't a bad idea either- it can be very contagious- if it's viral it will take a few months to disappear.
~Good Luck