Hi,
If you noticed blood in the semen, it is possible that the origin of the bleed could be anywhere between the testes and the urethra.
If there was no blood in the semen but localized bleeding from the tip of the penis, it could be due to trauma to the urethra or the glans.
It would be best to abstain from masturbation and sexual intercourse for about a week to give the injured tissue time to heal.
Complications of injury to the urethra include formation of strictures and infection and any trauma to the foreskin and glans can cause phimosis following infection or scarring.
Do keep us posted on your doubts and progress.
i really do suggest you go see a doctor. blood masterbating can be quite severe. but dont
go all freak out from this post.. i guess you should just take your time to find a doctor that can find out what your problem is.. ( it can be a prostate infection)