Since march, i have pain in the left side of my neck..not all the time ..but.sometimes the pain moves to the back of my head too..what you think?

Muscle spasm: This sounds like muscle spasm of the supporting neck muscles,actually quite common. I suggest using Advil or Aleve (naproxen) , if not allergic and also BioFreeze cram or gel.

Local Myalgia: Local myalgia includes muscle co-contraction and muscle soreness. Good rest, moist heat, passive muscle stretching and OTC NSAIDs will solve the problem. If pain persists after 2 weeks see your doctor for examination and tests.