That's a question of personal taste and genre that does not have a definite answer.
Obviously there are books in which sex happens but that don't tell of the sex itself, leaving it to the reader to infer it all from hints. And there are books that describe the taste and smell of body fluids in so much detail that what you eat while you read begins to taste of it.
There is a continuum from showing nothing to overwhelming the reader (or at least attempting to), not only in sex, but in violence, death, emotions, and everything else that humans do, think and feel. There is no right or wrong when it comes to content, only the laws of your country and the taste of the readers.
And the story you want to tell.
So the real question is: Is your story about sex, or are you allowing yourself to get sidetracked from the real plot into arousing yourself by indulging in sexual fantasies? Are you daydreaming, or are you writing? Because writing is not just the process of putting words on paper, but the craft of forming a coherent narrative.
If your sex scenes are like a cancer growing on the side of the story, disfiguring it, growing over it, overtaking it, then the sex is too much. If your sex enhances the story, drives the plot forward, brings the characters to life, then it is just right.
How can you tell?
Observe yourself. Do you enjoy indulging those fantasies? Or do you plan them to further your plot? I'm sure you can tell, if you take note of how you approach those sex scenes and how they affect you.
Outside of the romance genre, my approach would be to delete all the sex and see how little of it my story can endure to still work. I would then leave it like that: no more sex than is absolutely necessary.
Sex is like any other basic behavior: I don't let my characters munch on something to eat all the time, just because I'm hungry while I write. I mention food, defecation, personal hygiene and sex, only if those common behaviors are necessary for the plot. If they are not, I let readers assume that my protagonists perform them.
That doesn't mean that I don't relax from my real writing with an hour or two of having my protagonists f**k like mad, every now and then. I just delete it from the manuscript later.
If you are writing erotic stories, there is no too much. Or maybe there is? Porn without plot soon becomes stale. The most erotic stories I read didn't have a lot of actual sex in them, but they were sizzling hot because of how the characters got to the point where they had sex. Again, it seems, plot is king. Everything else needs to serve the plot, even in romance and porn.