What Causes Purple Colored Bump On Penis Post Intercourse?

A few days ago while having sex with my wife, I evidently ruptured a vein somewhere as I noticed purple swelling and a knot on the top side of my penis back towards the base. I was wearing a condom at the time and the knot is at the base of the condom. Swelling went down after a day, and the purple color has spread out and is starting to dissipate, however, spontaneous erections tend to occur less now. Just to see if things worked, we have engaged in sexual activity twice and everything works fine. The knot is still present and is about the size of half of a split pea, and stings slightly sometimes. What would be causing the knot and how long until it may go away?