In the absence of physical constrictions or hormonal issues, orgasm is largely about the brain. It's all about arousal, after all. Unfortunately, emotional and psychological patterning can block the arousal-to-orgasm trajectory. You may know the feeling of being in the bedroom and suddenly getting distracted by an email you forgot to send or a fight you had with a family member. This effect is especially intense when there is a history of sexual abuse, trauma, or shame associated with physical intimacy.
The important thing here is that because of the brain's neuroplasticity, our bodies and neural networks can be retrained. So consider what makes you feel aroused, and identify what path your arousal takes. Does it peak, then stop? Does it fizzle out? Does it never get liftoff?
Find a metaphor for what you'd like to happen instead. For example, if your arousal just suddenly stops mid-coitus, you might imagine instead the nonstop, exhilarating loss of control, akin to how you might feel on a roller coaster. Once you find the metaphor that you want, try meditating—or better yet, masturbating—while imagining your metaphor for orgasm.