Asking if the g-spot exists is a little bit like asking if God exists (but without the thousands of years of bloodshed and oppression). Even amongst those who agree that there is a g-spot there is no agreed upon definition of what it is or where it is. This makes arguing its existence more than a little difficult, as the skeptic may be using different definitions and criteria from the believer. So what do we know?
Most people who say that the g-spot exists agree that it is an area on the front wall of the vagina about 1/3 of the way in. There are several studies published in established and respected peer-reviewed journals that have documented changes in sexual response as a result of stimulating this area. There are also countless personal narratives from people who say that they have a g-spot, or at least who say that when they stimulate this particular area they experience a different kind of pleasure, which is very intense.
Some people who don't think there's a "spot" suggest that what's happening is simply internal clitoral stimulation. They don't deny that stimulating this area feels good, they just don't think there is an identifiable structure that can be called the g-spot. Still others say that if such a spot existed, anatomists would have noticed it by now.
From a sexual pleasure and sexual health perspective we might say that this question isn't very useful. We might ask; what does it matter if there is agreement that a spot does or does not exist? If you have discovered ways to feel sexual pleasure than that's great. And if stimulating a particular area works for you, and doesn't cause pain, then have at it. But if you try and try to "find" the g-spot and have no luck then perhaps your time would be more fruitfully spent trying something, or somewhere, else.