Eveyday when I wake up I feel pain in my neck (left side) and it stays for a couple of hours then it goes. It is very painfull?

Get checked. I would have your dentist or physician check it. It may just be a muscle but it could be something with a gland.
Few possibilities. Consider neck spine problem eg arthritis disk problem etc. Also pillow or some other objects might have irritated muscle by pressure-wrong position. See your doctor.