Each successive orgasm gets easier (vibrator only). Is this normal? (girl)

When I'm using my vibrator, the first orgasm takes a couple minutes. After that, I can cum every maybe 10 seconds or so, at least 10 times (I'll probably get sore at some point, but I've never tried to find an upper limit). On the contrary, if I rub myself with my fingers, I can only cum once because I get really sensitive afterwards.

Is this normal? I read somewhere that some other girls also experience the multiple orgasms thing, but 10 seconds seems kind of extreme... and also it's weird that I can only achieve it with the vibrator.