This also happens when my boyfriend fingers me. He rubs me hard, but sometimes I never reach an orgasms when he fingers me for so long. Can you help me?
It sounds disappointing, but I think you are about average. Orgasms really don't go on for a very long period of time. The female orgasm only lasts between three and 15 seconds for most women, though there have been instances where a woman was recorded as having a climax for a full 20 minutes, so that IS possible, but perhaps not in every woman.
For me personally, it seems like climax is more intense and lasts longer if it happens in a romantic environment, where my partner and I have plenty of time for each other without other distractions or waiting obligations of any kind. Also, he gives me oral, then stops before I climax, and then continues once the arousal goes down a bit. This makes for stronger orgasms when you finally reach a climax.