I first noticing about a year ago that when I masturbate I sometimes get a shooting pain in the side of my penis. It doesn't happen otherwise. It sort of feels like the skin is tearing, but I have enough lubrication and there isn't really anything leading up to the shooting pain. That area is a little more tender, and when unaroused I feel a ridge underneath the surface. You know how a big nightcrawler has that pronounced ring around its body in one place? That is what it feels like, but just on the side. I don't feel it when erect. There is also a large vein, probably the largest vein (to sight, anyway) in the thing, but it feels like the ridge is distinct from that vein. What could this be?