Left shoulder/arm pain?

I honestly dont know what it is. randomly i got a dull pain on my left shoulder all the way down to kinda my elbow its achy and dull i have some muscle cream on it. i have been sick with some sort of cold (iven been coughing up phlegm and runny nose ) for a week or so and im 14 years old male with anxiety but ive been taking medication for it and its been much better. im just wondering what the dull pain is the muscle cream in sorta kinda helping