Hi, you have a prostate infection,or either the making of one.I would get a PSA and also a mannual check.Dont know your age but I have know guys as young as 20 with prostate problems.It is not normal to have this problem and it needs to be checked asap.Good luck.
If your symptoms include fever, pain or swelling of the scrotum, groin, or lower back, of if you have blood in your urine, you need to see your doctor. You may have a problem with the male reproductive tract which may include inflammation, infection or blockage. The MD will order a urinalysis, a semen alalysis and culture and/ or an ultrasound of the seminal vesicles.
It happens, apparently fairly commonly. It's called hematospermia; you can google that term for more info. However, in a nutshell I can tell you it's almost always harmless... although if you continue to experience bloody ejaculate and/or pain it would definitely be worth seeing your doctor.