What you ask about specifically is your clitoris, which, along with other genital tissues, does typically shrink with the loss of estrogen—whether through menopause or some other medical event. Because you're under 40, which is young for what you're describing, I'd encourage you to express your concern to your health care provider and have a thorough pelvic exam. The exam will be helpful in finding out whether there's another vulvar condition causing the tissue changes—or whether you're experiencing normal changes.
As we lose estrogen, we do face something of a "use it or lose it" proposition. That is, circulation and stimulation keep our genital tissues healthier; left to their own devices, they'll atrophy. If you don't have a partner right now, a vibrator is a great choice to provide stimulation and increased blood supply to the area. Maintaining your health means you'll be ready for intimacy when—just when you least expect it—a relationship emerges!