I was lifting weights the other night, and didn't stretch (Bad, yes, I know) and when I went to go to bed, I noticed I had some pain right under my left pec, at the top of my rib cage. The pain starts there, and I can feel it going across my chest, toward my left side a bit. It isn't a constant pain, it only hurts when I move a certain way, for example, when I lay on my left side, I can feel a pulling/burning/stinging sensation in that area. It started two nights ago, and I can still feel it. Normally when I've pulled muscles in my leg, I could feel it for a few weeks.

Does this sound like a pulled/strained muscle, or something more serious? If it's something more serious, I don't want to wait around before going to see a doctor. How do I know if I should be seen?

Also, the pain isn't that bad at all. It's very minor, and it only aches when I lay on my left side, or move a certain way. It's not a pain that just comes and goes. I have NO shortness of breath or sweating either.