You should get this checked by your doctor. A possibility is a big medical term, Thrombosis of the dorsal vein of the penis. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2978449/ Here is something else and even more likely to look into lymphangiosclerosis. https://www.healthline.com/health/lymphangiosclerosis The description sounds like what you are talking about. Hardening of a lymph vessel or vein in penis. Have you been tested for std's recently or have any reason to suspect you should? The first thing they do is try to uncover why you'd have it if this is the diagnosis you receive. Treatment for that is then necessary obviously and when they don't have a reason to point at, they often will suggest no sexual activity and the cord becomes less visible and goes away on its own. But really, your best bet is to talk to your doctor.
Did you see the response? wondering if you still have this situation happening.