Hi.
As stated by u there are number of reasons for neck pain like incorrect posture, working on computer for long and reduced intake of fluids.
All this leads to pain and stiffness in neck muscles slowly leading to headache , Nosea and vomiting sensation.
Next Steps
start with heating of neck, stretching of neck muscles and strengthening exercises under supervision.
correct your posture while sitting and while working. Lot of information is available on net.
Health Tips
drink lots of liquid which is very important for reducing muscle stiffness