can't really orgasm with a vibrator?

so I can cum using fingers to stimulate my clit, but I've never been able to get there with a guy or a toy. I know vibrators are supposed to be a girl's best friend and all that, but I don't get it. My clit will feel really sensitive, then it starts to feel great, then I go straight to this feeling where all my muscles contract like I'll explode or pee. Even if I continue holding the vibrator there, I don't truly orgasm. I have worked on "letting go" more, the only result was that I peed myself and still didn't get the release feeling of orgasm (yes it was pee, I don't squirt). I'm still horny afterwards and it's frustrating for me. Any tips? am I the only one?