Why would my median cubital vein swollen the pain runs from my shoulder down to my fingers but the pain is more on the fold of right arm thanks?

Swollen vein: For the vein to be swollen, it has to be pressed upon by another structure or contain a blood clot.. Since you're also experiencing discomfort at the fold of the arm, I'm concerned about phlebitis of that vein. Has the vein been traumatized in any way? I recommend consulting your physician or a vascular surgeon for evaluation,diagnosis and advice.