For the past two weeks around about now, I've been waking up every morning with what feels like a muscle ache in the center of the chest - just below the rib cage and above the stomach. It kinda feels like I've pulled a muscle (which makes little sense as I am VERY inactive...) and every time I go to get up from bed, I notice it - I don't notice it during the day, except when moving my body awkwardly. Is this a muscular problem, and if so, why doesn't it go away?