I didn't have any luck until I was 21 (two years ago). About three months into my relationship with my current boyfriend, I had an earth-shattering combination orgasm during intercourse. I don't have those often, but after finding a partner I'm completely comfortable with, I almost always have multiples, either clitoral or vaginal, though those combination ones are more of a once a month thing.
On my own, I can't achieve multiples yet (possibly because I'm not very patient), but I'm usually able to achieve either a clitoral one or vaginal one about one third of the time.
I think, for me at least, you have to be very comfortable and not looking for an end result. If you set a goal and put pressure on yourself, it's less likely to happen.
