I get this same pain. I feel a tight sharp pain with I inhale. I have noticed that it is worse when sitting on a couch or squishy chair. It resolves itself when I stand up. I am currently undergoing some osteopath treatment and a few suggested causes were a pec minor tightness or the sac around the heart. Now, both have been treated and I still get this pain....so I do not really know. The doctors are confused about it too.