Why does my arm hurt like this?

My left arm, from about 4 inches above my elbow to about 3 inches below my shoulder, hurts. Just the muscle. It kinda feels like I’m shivering in that part of my arm, but I’m not cold. My house is quite warm. Earlier today, it was that part of my arm, plus the top-left quarter of my back. It feels so strange. I know nobody on here is really a doctor, but does anybody have any idea about what this could be? It’s really annoying. Thanks.