You say you can't orgasm on your own. Have you tried various self-stimulation techniques, rhythms, pressures, etc.? Are you being patient enough with yourself? Many women require 20 minutes of direct clitoral stimulation in order to reach orgasm.
If your technique is fine and you are giving yourself adequate time, then we must assume that you are in the grips of an inhibition. An inhibition is one way in which the unconscious mind protects us from feelings that are too frightening or unacceptable. Only you can figure out what is unacceptable or scary about allowing yourself to orgasm.
Here are a couple of possibilities: You were sexually molested; or you grew up in a sexually repressive household. Do some self-analysis, and you will find the origin of this inhibition.
Understanding is the key to resolving the issue.