It's been long time since one side of my neck hurts and i can't turn back my head like the other side.this problem continues till now.what can i do?

Could mechanical: Problem with rotation of cervical vertebrae in one direction with associated muscle spasms on the opposite side. It could also be a disk problem, but much less likely if you don't have shooting pain to the fingers on either arm. See an osteopathic doctor for a detailed physical exam on the range of motion of individual neck vertebrae as well as for imaging and a diagnosis.