I have a throbbing pain left back of my neck going to the top of my head to the left side of forehead, should i be worried?

Probably not: Though a simple musculoskeletal neck pain, with perhaps some irritation of the occipital nerves, is most likely cause, only an evaluation by your doctor can rule out more worrisome causes.

Muscle: Go to your md and find out if your pain is from muscle tension.

Multiple Causes: Muscle spasm or strain is a likely diagnosis. Others to consider would be occipital neuralgia although the forehead symptoms are a little harder to explain. If it continues, i would suggest getting evaluated.