Are you on any medications that might interfere with your sex drive? SSRIs in particular are notorious for this.
Failing that, your masturbation habits here are relevant. If you've watched a lot of porn in your life as many people have, or watch it frequently, it's quite likely you've just become desensitised to the kind of images that used to induce arousal, as well as, hopefully, hit the limit of intensity or extreme content that you're willing to watch and now have nothing else left that you don't just find uncomfortable and disturbing. If this sounds like a possibility, it's a good thing - it means your brain is just starting to hormonally cut you off rather than urging you to seek out more and more extreme and morally questionable material, as some people do with pretty dark consequences.
Whether you are watching porn or not - your frequency of masturbation is also relevant. Because of an annoying but unfortunately evolutionarily necessary quirk that causes our brains to basically gradually reduce the level of pleasure we get from absolutely any pleasurable activity, too much of anything will lead to that thing getting less and less enjoyable until it's just, frankly, boring, and the reward is not worth the effort.
If you masturbate literally every time you feel horny - you need to start masturbating less. Channel that energy into something else to distract yourself for as long as you can. If you're watching porn - watch less of it, in fact try to just take a long break, I'm not telling you to stop entirely although there are arguments to be made for that idea - but, really, just set some limits so that masturbation actually feels like something special again, a rare treat, if you like, rather than something you do so often that it's not even interesting anymore. That would be my take on it anyway, if I'm missing any important details, please share.
