How are you? What other symptoms are present? Superficial thrombophlebitis or inflammation of a vein just under the skin and presents with swelling, redness, and tenderness along a part of the vein. A small harmless blood clot may develops inside the inflamed part of the vein, and the vein may then feel hard or knobbly. This occurs for no apparent reason but a slight injury to the vein may be the trigger. If this persists, it is best that you have this checked by your doctor for proper evaluation. Take care and do keep us posted.
I had a superficial clot in my left arm where an iv was placed and it didn't show up until I did some exercise at home with my arms. Then it showed up an hour later with redness, swelling and pain near the site. I was already on warfarin for a dvt in my leg at the time. They say not to exercise if you have clots as this can move them to your lungs, heart or brain. I would go to a doctor and ask them to check you out to see what caused this.