The term Myalgia simply means pain in the muscles. It can be due to many causes. In your case it’s affecting your neck and back. It is better to seek atleast one good opinion from a physician as to ascertain the cause of muscle pain. In your case, prolonged sitting in front of computer may be responsible. Please take a good note of your chair, its height vis a vis monitor, posture that you adopt while sitting and how long you work continuously. Little modifications of these might be rewarding. For myalgias of unspecified cause, any non -steroidal analgesic can be used but preferably should be used with caution as all share gastric side effects and prolonged used can be harmful. Certain muscle relaxing drugs can also be used at times if muscle stiffness/spasm are prominent. Please consult your physician.