I have pain in deep in my bicep, my whole left shoulder, and neck. What is actually messed up?

About 3-4 months ago I was kickboxing and hitting a bag I went for a kick and slipped and landed on my left shoulder. I had pain for about 2 weeks but it went away. Now many months later I have the same kind of pain but instead of just my shoulder area it is in my bicep, shoulder, and neck. It hurts all day no matter if I move it or not.