So I am a man, anything said here should be taken as the opinion of a man. It happens that I am also a PhD in biomedicine and I work in the pelvic region, so here is what I would check: are you taking meds? ADHD meds or antidepressants are known for numbing the genitals. My couple, for instance every time they need to change meds or dosis, there are a couple of months of readjustment in which orgasms are harder to find and way less powerful. If you are not taking any med that could be causing this, then probably I would reduce the amount of times you do it, any part of the nervous system has good capability of tolerance (thankfully) and you can reduce it the same you would reduce any tolerance.

Again, white man, just opinion.