Crazy periods, sleepless nights, and (uh-oh) painful sex. Welcome to perimenopause! How to ease the symptoms and feel like yourself again.

Two years ago, at age 37, I went from being an easygoing, upbeat person to a candidate for town crank almost overnight. For five days each month, I would lose my temper over the most minor things. Concerned, I asked my doctor for help. My symptoms, he said, sounded like they might be connected to perimenopause—the transitional period, lasting anywhere from four to 15 years, that leads up to menopause.

Some 21 million American women are in perimenopause right now. And many of them are grappling with symptoms that range from mildly annoying—like mine—to virtually incapacitating. Think hot flashes, irregular periods, vaginal dryness, insomnia, forgetfulness, and more. “Many women feel like their body just isn’t their own anymore,” says Alan M. Altman, M.D., an assistant clinical professor of obstetrics, gynecology, and reproductive biology at Harvard Medical School, in Boston. I know what he means.

Unfortunately, doctors still don’t fully understand perimenopause. But they know much more than they did when our mothers and grandmothers went through it and therefore can do more to help us. (After I went on a low-dose birth control pill, for instance, my symptoms eased.) Here, answers to common questions about what experts dub “the storm before the calm.” Why am I having these symptoms?

It’s simple biology: Your ovaries are aging, but the pituitary gland in your brain, which governs reproduction, is determined to keep you fertile. Every month, your pituitary produces the follicle-stimulating hormone (FSH), which prods your ovaries to produce mature eggs. If an egg isn’t released on schedule, your pituitary churns out more FSH to correct the problem. This may or may not work—meaning you may or may not ovulate. In any case, your production of estrogen and progesterone becomes erratic.