Can do. I'm not sure what's unclear, so I'll cover my bases.

Endometriosis - as part of the period cycle, the layer of the womb's walls that's inside (endometrium) thickens, ready to take a fertilised egg, but if there's no egg (or none in time) make itself a cozy home among that lining, then it sheds, and is ejected from the body along with blood during periods. Endometriosis is a disease where that lining starts to grow elsewhere outside the uterus, most commonly around it, but can end up all over the body, even inside lungs or growing on skin. And, of course, it makes periods quite a bit more painful. Current estimate is that it affects 10 percent of menstruating people, yet it's regularly misdiagnosed or the diagnosis is delayed, leading to years (if not a lifetime) of pain. This article is a good read on the troubles with endometriosis.

The research about its effect on men or another one about how endometriosis affects the sexual wellbeing of men - even though over the recent couple of years there's been an increase in the number of studies on endometriosis, it's upsetting to people that instead of focusing on better diagnosis, care, alleviation, etc, people are still looking into "but what about the men 🥺". Not to mention the biased / lacking variety selection of participants for existing research. This all ties into medical misogyny and women's concerns being consistently dismissed (see more below).

On period pain - this article is a good read (anti-paywall proxy), but in a nutshell, it is so "normal" that people have pain during periods that people just suffer in silence, or are dismissed when they do try to seek help. There are some materials (example, example) online, though even official materials can downplay period pain, which is just an example how normal and systemic it is, though one should not be surprised as half report their symptoms/concerns being dismissed. Which also ties into endometriosis, since it can increase the painfulness of periods, to the point of being debilitating. Not to mention the general dismissal of people's pain in gynecology, what with for example medical professionals underestimating pain and just not offering pain medication.

On the cervix - things have gotten better in gynecological care in more recent years, though there's still a lot of room to grow. In Sexual Behavior in the Human Female (1953), Kinsey’s group wrote that the surface of the cervix is "the most completely insensitive part of the female genital anatomy." based on a reaction to a gentle stroking by a probe. And then, it was taught to doctors for years, decades, and some healthcare providers still keeping to the old beliefs. It's obviously wrong (ex. a neat read on cervix and pleasure), but what do you expect, the doctors no longer use the word "hysteria", but medical misogyny is sufficiently embedded that just slapping on a generic diagnosis is a thing.

Did that clarify things for you or is there something more you'd like to know?