I think I might have had a problem with that once. I went out with this really, laid-back stoner guy from West Virginia several times. Well, on the second date he let me know that he was really interested in fucking me... Let me tell you what, this laid-back stoner guy turned into a demon in bed and nearly fucked me through the bed. I felt raped. It was sorta hot, but I'm never been fucked so brutally in my life. He kept banging my hole with his 8.5 and "hitting bottom". It was painfully, mostly. I didn't get a chance to cum then & there, I just wanted out of there before be decided he wanted more...LoL. That evening when I jerked off, my cum was bloody. Scared the crap of me. All I can figure is that he hurt my prostrate, bruised it, scratched it... I've never had a problem like that before or since.
Odd that no one has said that it is not the prostate itself getting *directly* getting massaged, fucked, etc., but the location of the prostate gland behind the rectum. So, it is your rectum that is subject to any damage. Other than the pleasure derived from prostate stimulation, each individual man may have a different reaction from how hard that area is worked over (e.g., the violent pounding). The prostate is a gland and is surrounded by nerves, muslces, etc., and as such can produce other than just fantastic orgasms. Some men have trouble urinating after being fucked. Also, chances are that when he "hit bottom" you probably clenched your ass muscles. Because they are not use to a hard cock being there, you would probably be sore for a while. Blood in your semen is a whole different issue. If there was a small amount, it may be some small blood vessals that broke and that is actually common, even after athletic competition out of the bedroom. However, if it was a lot of blood, I am not surprised that it scared you because that is not common. I recommend you see a doctor and get a prostate exam that every man should be routinely getting anyway.
Finally, sex should not be painful. If it is, you need to speak up and tell him to allow you to either change positions, make him slow down, or you need to learn to say STOP. At some point a guy saying "You just have to relax" repeatedly means he just is not for you. The fact that you felt raped means just that, you were. Better luck on your next date.