When ejaculating i noticed a small amount of blood in my semen. there is a small itch like pain on the left side of my penis. should i be worried?

See your doctor: A small amount of blood in your ejaculate is most often not anything that will damage your long-term health, but, especially with other symptoms, may be a serious infection that needs to be treated. See your doctor and be open about your sexual history, or go to your local youth clinic or testing site (like city clinic in san francisco).