I was waiting in line at the movie theater to buy a ticket to see Harry Potter and the Half-Blood Prince when I got a text from my sister: “Giving tampons a try. Having trouble. Can I call?”

It was the summer of 2009, which made me 23 and my sister 34. She’d been calling me to talk about tampons all week. She and her family were going on vacation in a matter of days, her period had just started, and she had three young children who were excited to swim. She’d only ever used pads.

Since she didn’t want the people waiting in line with me to hear the gory details of her tampon struggle, I waited to call until after the movie. By that point, she’d given up.

“I have no idea what I’m doing,” she said, emphatic. “The instructions are confusing, and it just feels like I’m doing it wrong.”

I pushed for details—delicately, with lots of euphemisms, since we weren’t a family who talked frankly about our genitals (which the exception of my father who, after being diagnosed with prostate cancer, now talks cheerfully about his “prostrate” to anyone who will listen)—but she kept repeating the same thing: “I don’t know. I don’t know what I’m doing.”

Now, six years later, my sister texts me again with a question about tampons. This time it’s because her daughter is having trouble with them.

“How old were you when you started using them?” she asks.

I’d gotten my first box of tampons not long after my first period at age 10, but it wasn’t until I was 18 or 19 and started masturbating with dildos that I finally figured out what the hell I was doing. My problem was, I suspect, the same as my sister’s had been and now my niece’s: everything between my legs might as well have been a black hole for how little I knew about it.

These days it’s generally well accepted that American sex education is laughable, and my school certainly wasn’t the exception.

Internal reproductive organs were fair game for discussion. We were shown diagrams, slideshows, and videos of how sperm fertilizes an egg, how the egg moves through the fallopian tube, how the lining of the uterus “sloughs off.” (That was the verb my anatomy teacher used when we reached the reproduction section of the curriculum. He stuck doggedly to it throughout the entire lesson, refusing to use a synonym even when he was asked to clarify, probably because that was how our textbook worded it: “During menstruation, the uterine lining sloughs off.” What does that mean? I wondered. After school, I went home and looked it up on the internet.)

External sexual organs were off-limits entirely.

I learned to masturbate by holding something between my legs and humping until it felt good. In high school, I discovered porn online, but the only thing I could discern from the clips I found was that there was a gaping hole between a woman’s thighs that a penis (or two!) could fit into.

My first box of tampons (part of a free kit sent by Tampax to Seventeen magazine subscribers) came with a diagram of a woman’s genitalia. Everything was peach-colored and perfectly oval-shaped, like it had been drawn with an MS Paint tool, and I couldn’t see it as a reflection of my own body no matter how hard I tried.

Because of all this, I mistook my inner labia for my vagina for years. Probably the porn was especially to blame, since it gave me the image of a gaping hole rather a small one capable of stretching. Not that I hate porn. Quite the contrary, I’m a big fan. But it’s not how a teenage girl should learn about her body.

I commiserate with my sister and niece. On the phone I tell my sister, who passes the information to her daughter, that it took me years to figure out how to use a tampon. (I consider mentioning that I use a menstrual cup now, but I decide against it. I can hear the disgust in my sister’s voice clearly enough in my imagination that I don’t need to hear it out loud.)

We chat instead about the general inconvenience of menstruation. She confesses that she started bleeding more heavily after she had kids: enough to completely fill an overnight pad in under an hour.

“That doesn’t sound good,” I tell her. “Maybe you should see a doctor.”

“Nah,” she says, “it’s just from having three kids. It’s pretty common to bleed more heavily after childbirth.”

I envision how many pads she must be going through each day, how quickly the cost of those pads adds up, the amount of time she’s spending in the bathroom changing her pad, how much focus she must be devoting to worrying about whether the pad is full yet or what will happen if she can’t get to a bathroom in time and ruins her clothes. Not to mention all the iron she’s losing.

“Still,” I insist, “that’s a lot of blood. I really think you should talk to someone about whether it’s normal or not.”

“Oh it’s fine,” she says. “It’s just my stupid body. I’m used to it.”