It was a standing joke—literally—between Chucho and me. He would pass me in a doorway, our bodies brushing against each other, and suddenly grab me in a crushing embrace, panting, while I smiled sheepishly and waited him out. Then he would pat me on the hindquarters the way you might a favorite horse, and we would go our separate ways.

But as two months postpartum turned into four and six and eight, my libido stayed stuck in neutral. We tried, once in awhile, to rev up the engine—we dimmed the lights, bought a new tube of K-Y jelly. But nothing could get me past the thought that this contrived, paint-by-numbers kind of sex was taking up a lot of prime sleeping time.

What, really, was the point? I felt like Andie MacDowell in Sex, Lies, and Videotape, when she admits to her therapist that she doesn't masturbate. "It just seems so stupid," she says. I must point out that this is a rare phenomenon in my 15-year marriage, which I would optimistically guess (based on no comparison data) is sexually healthy. Certainly our sex life has changed over the years, which I take as a sign of growth. We aren't the same people who used to scramble home for a quickie on our lunch hour, but as we approach middle age, the comfort of our long acquaintance has made intimacy more, well, intimate.

We wrecked all that by producing Lucia, an unbelievably happy baby. Her older brother and sister had been challenging infants, but Lucia was a dream: flexible, easy to entertain, a good sleeper. All through the pregnancy I had sworn this was my last one, and meant it. I was 37 years old and three children were enough. Then, after Lucia's blessed arrival, I began to feel an odd kind of grief: The exquisite and bitter pain of knowing I was doing something I loved for the very last time.

I clung to the last of my pink, precious baby days—the tiny onesies, the soft little cheeks and toes, and especially the hours spent nursing in the rocking chair. Breast-feeding was a love-drug for both me and Lucia. We cuddled together day after day like a mama bear hibernating with her cub. We didn't need anyone else. Breast-feeding, of course, was the root of my libido problem. All the baby-care books explained how the hormones that made me produce milk were also shutting down my sex drive.

To fix this, the books suggest the same old stuff: Make time for sex, dress up and go on a date with your husband, buy nice underwear. This advice just seemed silly. How could movies and lingerie counteract my own body's chemistry? Still, I felt guilty that I no longer turned to my handsome, passionate husband in the middle of the night. I knew it couldn't be fun for him to be married to someone who was no longer interested in some of his favorite and most satisfying impulses.

I began to detect an increasing irritation in him—a shortness, a shrinking of generosity. He started pointing out my driving errors. His sarcasm got sharper. It took me awhile to connect his peevishness with my libido problem, but once I figured it out, it made sense. He felt rejected, and it made him mad. I must add that I hadn't exactly been a peach to live with. Even a dream baby requires a lot of care, so by the end of the day I wanted Chucho not as a lover but as my own personal relief worker. Evenings, after we got the kids squared away, we took turns on the computer and went separately to bed.