pinched nerve possibly muscles spasms also possible I have degenerative disks in my neck which cause a neck rt shoulder cervical syndrome with the same symptoms but that doesn't mean that's what you have.. you should get an xray and see your doc, you didn't mention if there has been an injury or strain or overuse ?
Have you been very stressed out lately. Have you been on the computer for a while. Your neck could be very tense leading to neck pains. Just try to exercise your neck muscles lightly.
I am fused from 2 thru 6,10 screws and a chiropractor about 2 weeks did 2 xrays and it showed my c7 disc channel very narrow where the nerve goes thru