What Causes Cramps Like Pain In Left Neck, Back, Shoulder And Arm?

I have been having cramp like pain in my left neck/back/shoulder/arm. The pain moves and changes intensity. I had my heart checked - no issues, they said it was probably just a muscle strain and would go away. Two weeks of taking ibuprofen and it still hurts. Alternating heat and ice and both reduce pain. I feel like it may be pinched nerve. How do I find out and what are treatments?