cord under armpit

[Trishh]

I am at wits end. I have been on a 5-week journey to try to resolve this. After a light workout at a gym (was doing rows and not sure if this is even related), i noticed the next morning, a cord sticking out of my armpit, sensitive to the touch. the pain traveled along the inside of my arm to my inside elbow over the next few days. went to my orthopedic guy who checked me out and said that there's nothing wrong with my tendons, bicep, tricep, ligaments,etc, and he sent me to a vascular surgeon because he wasn't thinking that it was a tendon - so must be a clotted vein. But the vascular surgeon said it doesn't look like a vein. i have taken three ultrasounds now over the past 5 weeks, all negative for deep vein clots. During this time, this "cord" has now bulged out past the elbow, down the forearm, and all the way to my wrist. It's as if this cord(vein or tendon?) has lost its elasticity. Starts to hurt like a stretched rubber band, preventing me from fulling extending. MRI was negative as well. the Dx by default is superficial vein phlebiitis but a second vascular guy yesterday still maintains that that thing sticking out of my armpit, elbow, etc, does not behave like a vein, and the ultrasound doesn't show it to be a vein,"but what else could it be?". So he prescribed 800 mg motrin.Very disconcerting to have this thing sticking out and affecting your movement, and no answers. Any ideas?