What Causes Pain And Swelling Inside Upper Left Arm?

I have a throbbing pain on the inside of my upper left arm. It started 5 days ago. It felt lymphatic, and as of today, the lymph node on my inside elbow is swollen. I am also having trouble with what feels like oxygen intake, not necessarily breathing, just don't feel like I can get my lungs full (at rest). I play sports and exert myself and do not notice it bothering me when I am active (the breathing). But my arms hurts when I lay down. How's that for a bag of tricks ;-)