Why cant i do an orgasm?

i am a 26 year old woman ,since i started have sex, i have have a hard time have orgasms with my partner. event of fact the with the sole purpose time i can do this with out my own help out, is if im on top of a hulking man. i have no problems when i masterbate. anyone else experiance this problem?Why cant i do an orgasm?
When you are on top, the angle of pentration is different, so that's why it's easier for you to own an orgasm.
Also, when you're on top, you're in control, and you can perceive out what speed/angle works best for you.
You should have your partner experiment next to sex positions at different angles (so the penis hits the Gspot, or the male pelvic bone stimulates the clitoris during sex), and communicate near him what the best angle, speed, and depth of penetration works best for you.
Most women stipulation clitoral stimulation to orgasm. During sex it is perfectly mundane to help the guy out.
sometimes its a control issue you enjoy to work through. Sometimes takes me longer to orgasm clitorally unless i sustain but its gotten better the more often things are practiced ;) Sometimes, at tiniest during sex, things aren't always rubbed right to orgasm..