I'm 13 and I had a wet dream for the first time. It was suprising that included a blood stain. I don't feel any pain. My parents are worried.
There are several possible causes for blood being in your semen, such as having an infection, having kidney stones, or having taken a hit earlier. Most of the time the problem resolves itself as the body heals. If you continue to find blood in your semen, then you need to see your doctor so he can find the cause.