I am a 19 year old boy and for the past 2 days while walking home from class (yesterday at 5:30pm, today at 3:45pm) I got a sharp pain in the left side of my upper back just out of nowhere, no warning, and no reason why this would happen. I haven’t been exercising other than walking so I don’t see how I could’ve pulled a muscle, I have struggled with anxiety in the past but I can tell that is not what this is (plus I haven’t felt anxious at all recently.) It hurts so much I can’t take a deep breath in or laugh. Is it a growing pain? Why am I fine all day until walking home in the afternoon?