My first thought was pleurisy - as I've had it a couple of times... But if it's not a sharp pain, then you're probably correct that it's not pleurisy.
Is it worse when you wake up in the morning? Is it impacting your daily activity? Is it a dull constant pain or does it come and go? I'm sure you've racked your brain trying to figure out correlation to anything...maybe give your doc a call and see if they can offer suggestions?