Could be a break in the blood vessel, from too much pressure. It will most likely continue to do this, as long as you create pressure to your shaft through clamping.You may have to lay off, for a few days, then have ago after the time off, to see if it's healed.Keep us informed.
Girthius is probably right about a break in the blood vessel. I don't know if time off is absolutely necessary however...as long as you're not feeling any discomfort whatsoever, then I would believe that you're okay to continue. You may want to go light on the clamping for a few days, but I think completely stopping for a few days isn't necessary.
I had something similiar and had a week off as I felt it was stopping me from being as intense at my workouts and only slowed my gains down. Once i resumed i could go full on again and gain better than ever.
I think a week off would do you good, whats a week off to cure it in a lifetime of Penis Enlargement compared to a disfunctional dick for a life time???
Sorry to be a scare mongerer but as the sayings go, prevention is better than a cure and better safe than sorry.