Me and my mom were moving heavy stuff like furniture and stuff and there was this really heavy box i lifted and moved. It didint hurt at first but i could tell it was heavy and i think i strained my arm. But then the next day my arm was really sore it was sore in the upper sholder part. I thought that i pulled it and it would get better in a few days. Its been about a week and its still hurts i can only lift it like half way and it hurts. what should i do? and is it a pulled mucle?