Most common reason for neck pain is disk problem. It may lead to pain in shoulder and along entire upper limb due to pressure over nerve - this is called radiculopathy. Only when you have severe radiculopathy, MRI to be done immediately. Otherwise you follow medicine, neck exercises and postural advice. if pain persists or increase then MRI can be done later. This is mainly an orthopeadic problem, consult Ortho. There are so many other reasons for neck pain, but are rare, needs evaluation.