Over the past month or so, my penis has been developing noticeable red and purple spider like veins on the skin. They are mostly only visible when I stretch the skin out, or when I am erect. The largest of the veins are slightly tender when I am erect and kind of hurt when rubbed over. The pain isn’t bad, they just feel tender to the touch. Any idea what this could be? I was recently checked for all STD’s after I received unprotected oral sex. All came back negative. It was after this unprotected oral sex that this all started. Picture below.