Chaunie Brusie is 27 and pregnant with her fourth child.

Brusie's other three children are younger than 5. While the Babble.com blogger is happily married, she has felt a strain on her sex life.

"Pregnancy for me does not feel like a sexy time at all," she said. "It just feels like we really need to get through these nine months … and get this baby out."

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Brusie is one of the millions of women who have lost interest in sex. For her, the issue might not be exhaustion, but the pregnancy itself.

Dr. Lauren Streicher, a Chicago gynecologist and author of the new book "Love Sex Again: A Gynecologist Finally Fixes the Issues That Are Sabotaging Your Sex Life" says a hormone called prolactin could possibly be dousing the flame.

Other causes could include diabetes, depression and even birth control pills.

"So many women come to me saying I'm their third, fourth, fifth opinion for a problem that has really been impacting on their relationship," Streicher said.

The book aims to shine a light on the physical and medical conditions that affect women between the sheets.

Many women simply live with bad sex instead of searching for an answer.

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"They're just embarrassed to bring it up and they also minimize the importance of it," she said. "You go to your doctor once a year and you think, 'This is not a subject that I should be spending my limited time talking about,'" she said.

For Brusie, realizing that her loss of mojo is temporary has helped her get through it.

"It's hormones, it's breast-feeding, it's not just me," she said. "It doesn't mean I don't think my husband is attractive or I don't love him."