Have sever pain in my neck and shoulders that rums down my right arm into my hand. Now starting on left side. All after C4 & C5 neck surgery.?

Talk to your surgeon. This could be postoperative swelling of the nerve, irritation of the nerve from surgery, or other causes. The best way to know is contact your surgeon. He will best know all the details of your surgery and what you should expect.
Needs Evaluation. The pain may indicate adjacent segment problem (c5-6) which would typically radiate down to the hand - thumb and index finger. You may need additional imaging to check for this. It can occur in approximately 25% of patients with cervical fusion over 10 years.
Get checked. You would certainly want to make sure your surgeon is aware, especially if you had recent surgery. There are rare perioperative complications such as epidural abcess or hematoma that can worsen symptoms. If your surgery was some time ago and you initially did well, your problem is most like related to adjacent level disease. Thank you for your question.