Female orgasm

[Berryberrywintermedley]

I always orgasm with a vibrator and clit stimulation which doesn't bother me at all and is what I like and I incorporate into sex
Most of the time I can finish quickly but sometimes I will struggle to get there and I won't feel as many sensations as usual and sometimes I won't get there at all.
Normal?

Don't think one can ever class something as normal these days. You gotta give yourself the capacity and range to set your own normal.

There can be so many factors to any intimate experience, being environment, time of day, what's on your mind. If you say it's only sometimes, then see if you can gather more "data" and reflect on what could be the factors leading to a less "optimal" expereince :)