Peyronie's disease is one of the most common causes of sexual pain in men, affecting an estimated 1%. The characteristic sign is a visible curvature or hourglass shape of the penis when erect. Physical damage to the penis causes plaque and scar tissue to build upusually on the top of the penis, resulting in an upward curve.
"If the penis is bent or twisted, it can tear the fibrous tissue casing that surrounds the erection chambers and cause a laceration in the tissue," says Ira Sharlip, MD, spokesman for the American Urological Association and clinical professor of urology at University of California at San Francisco. "When it heals, scar tissue forms, and eventually it forms plaque."
Another possibility is that your penis was fractured. "If your sex partner is on top and comes down on the penis but misses, the penis will bend," says Irwin Goldstein, MD, director of San Diego Sexual Medicine and editor in chief of The Journal of Sexual Medicine."If there is enough force, it will fracture the envelope. Then inflammatory cells will try to repair the fracture, bringing pain and scar tissue."
The pain from Peyronie's disease can be quite debilitating each time a man experiences an erection. It can even affect his ability to sleep.