question: Hello, my girlfriend is 31 years old, 5 feet 6 inches, and 125 lbs.  She discovered a lump on her arm two days ago.  The lump is underneath her skin, toward the inner bicep and just above her elbow.  At first it was painful when pressed and has become more tender since.  Over the past two days it seems to have grown and is now about 1/3 the size of a golf ball.  It is red and does not move.  Any idea what this might be?  Thank you.