I read a book half way through about interpreting dreams, so that makes me an expert, right?
Well anyway, I've read that sex dreams often aren't really about sex...but then again, rape isn't about sex, it's about power. allofme has a good point about the trust. Who does the person in the dream who is raping you remind you of in your real life? Maybe whoever it is in the dream is telling you don't trust them as much as you lead yourself to believe. Or maybe this person is somehow dominant over you, a boss or supervisor, so that domination in your dream is relived by you being raped. Maybe you are being dominant over another person and are feeling guilty about it. Just some theories. i would think about things like what you feel guilty about since you've had these dreams, someone who has done something bad to you that may cause you to feel dominated...something along those lines maybe.
Who knows, dreams are weird and I don't think we'll ever fully understand them.