Why when having sex can i only have an orgasm when i'm on top?

Many possibilities: They say that position is everything. Your orgasmic potential may be related to the way in which the penis is contacting your clitoris or moving your labia so that the clitoris is stimulated more, but this may also have psychological implications, and being on top is therefore more satisfying. If this concerns you greatly you might see a clinical psychologist or sex therapist. Have many more.