Sex drive differs from person to person. Sexual desire is based on many factors: physical health, sexual beliefs, current relationship and more.
For men and women, lack of emotional intimacy can cause a lack of desire. If you're in a relationship, try setting aside time with your partner to rekindle and reconnect. Make a weekly date. Communicate about sex and discuss what you like and don't like. Try different sexual positions, sex toys and fantasy to recapture your sexual desire.
If your lack of interest in sex is distressing, you might want to talk to your doctor. Your doctor can take a look at your current illnesses and medications to ascertain if a medical problem might be present. A doctor might perscribe changes in diet and exercise, Kegel exercises, or medication.
Experimenting with sex toys can introduce you to new sensations and boost your libido. Women can try simple, powerful vibrators like the Acuvibe or the Lelo Iris Vibrator. Men can try male masturbators like the Tenga Squeeze Play. Sexual enhancing gels like KY Yours and Mine can also add more sensation. The more you masturbate and enjoy your sexual responses, the higher your libido will become.
If you're perfectly happy with your low sex drive, you may be an asexual. There are a growing number of advocacy organizations and resources for asexual people available online. Some asexuals continue to have romantic relationships that comprise most every part of a traditional relationship--just without the sex. If your lack of interest in sex causes you no distress, there's no reason to force yourself into masturbation or sexual activity.