Im 15 hurt my top left back muscle please help maybe from working out?

Ok well iv been working out since the beginning of the summer. and this monday i was working on my shoulders and after workout i played soccer everything was fine i went on couch for about 2 hours kinda leanned on my back left shoulder like on my back. and it hurt when i got up. the muscle is like bellow my left shoulder on my back. and it hurts so i stopped working out for a bit.. it got hurt monday its now friday and everyday it was getting better and less sore and today it started pinching and really bothered me its acting so fragile/pinchy today.. and i was planning on working out soon but i didnt want to benchpress and drop the bar on my chess because of a pinch in my back. please tell me what it is. and how to get rid of it. thanks