Hi!
If it just started today, it could be muscle strain and stiffness due to work. Gently massage your neck. Apply local analgesic gel. Do rotatory neck exercises. Do shoulder and upper back exercises. If these increase the pain, then show this to a doctor. Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.