Thorn in my Side

So I hurt my side a week and a half ago. I'm not sure I know how it happened. I had a sharp pain in my side and I thought I must have somehow fractured a rib. I couldn't breath more then shallow breaths without causing pain. After about two days it got a little better and my only conclusion is I must have pulled a muscle in my side. I have no idea how I did that. It's still bothering me. I started going back to the gym but my movement is very limited I can't make deep breaths. It hurts to twist my upper half and I have to try and not do that. I wonder how long this is going to take to heal.