Yes, it's very common. G-spot stimulation can be a tricky beast and even for some women who try and try, it may never happen. You can get shots to puff up the area but most women I've spoken to claim that doesn't really do much. Some women can only do it after intense intercourse and additional vaginal and clitoral stimulation.

It took my wife sometime to have one even though we/I tried all the time. I finally let her get on top and told her to just do what felt good. That worked like a charm, mostly because I think she was not so much trying to have a G-spot O but rather enjoying the stimulation she was receiving.