What to do about neck pain radiating to shoulder and arm

[SkyLemon]

I recently had leg craps and pain has appeared in my neck, on the left side, where the neck meets the shoulder. I was told I may need to eat more magnesium and potassium, which I started doing. The neck pain radiates across my shoulder down the top of my arm, to my elbow. My arm feels tired, if I lift it a long time, a sore feeling. But the sharp pain is on the neck itself.

I've been massaging my neck, taking hot showers with water on my neck, using one of those pillows you can heat and wrap around the neck. I thought perhaps I just pulled a muscle and it will get better with time. But it's been over 2 weeks now, it hurts very much and not getting better.

What do I do?

Thanks in advance for any help and advice!