The jokes around the phrase "not tonight honey, I have a headache" are endless. But, when this sentiment becomes a fixture in your relationship, it's no laughing matter. "Most sex therapists would agree that of all the problems presented in their offices, the largest category of concerns are those centering around levels of sexual desire," states Dr. Robert Birch, a certified sexologist and family therapist.

When you and your partner are sexually out of sync, as Dr. Birch puts it, several factors are at play. These range from trouble in your relationship to medical problems, job stress, medications, psychological problems, cultural and religious issues, and sexual dysfunction. With so many possible causes of sexual incompatibility at play, it's no surprise that there's no one or easy solution. Here are a few tips to help you connect on the same sexual wavelength as your partner.

Communicate your needs. Is your partner aware that you're not sexually satisfied? If the lines of communication are closed off in other areas of your relationship, it will probably be more difficult to discuss your sexual needs. Phil McGraw, host of Dr. Phil and bestselling author, recommends that you identify your needs first. Approach your partner when you're both calm and rational. Be specific when communicating - and don't play the blame game.

Take the pressure off. Don't reduce your relationship to just sex. Focusing on the incompatibility of your sex drives will only intensify the problem. Since the "free love" era of the sixties, it seems most of us think we're entitled to great, passionate sex. While sex helps us to bond and feel closer to our loved ones, it's only one component in a healthy relationship.

As you start to communicate your sexual needs more to your partner, continue focusing on the areas where you are compatible. Spend lots of "loving" time together without the expectation of having sex - have romantic dinners, hold hands, send each other love letters or naughty texts, or go salsa dancing together. Just enjoying each other can fuel your passion and help to put you more in sync.

Check your stress levels. While several studies suggest that sex can lower stress, on the flip side, too much stress can dampen your desire. When your body releases too much cortisol, it can lead to chronic stress. This affects your thyroid function making you feel more fatigued, lowers your immunity so you're more susceptible to infections, and prevents you from relaxing - all of which impact your sex drive.

Try to resolve any particular issue that's stressing you out, such as your finances or your job. Also, include stress-reduction activities in your daily life, such as meditation or exercise. Exercise actually releases feel-good hormones that can increase arousal.

Schedule your lovemaking. Sometimes your sex drives may not match up because of timing. For instance, some women experience lower libido when they're suffering from premenstrual syndrome (PMS). Or, you may feel more exhausted on weeknights when your partner is feeling frisky, so weekends may be a better time to have sex. Being flexible (no pun intended) is important.

It may sound less romantic, but several sex and relationship experts recommend setting scheduling sex. They suggest it takes the pressure off and creates a sense of anticipation. But most importantly, regular sex keeps the fires burning. According to a German study, no sex leads to less sex. People who have sex less than once a week take on more work to fill the void - which could be filled with more lovemaking instead. It's a vicious circle. Penciling in a few hours each week for passion can prevent your sex life from fizzling.

Spice things up. It's possible that the problem isn't with your or your partner's sex drive, but with your sex life in general. The old adage "variety is the spice of life" rings true when it comes to sex as well. If you've run out of ideas, there are countless books and videos dedicated to helping couples enhance their sex lives. Explore each other's fantasies (as long as you're comfortable) and be open to new experiences. Sometimes a simple change of venue or different time of day can rekindle your desires.

Assess your diet. If low libido is the problem, consider adding aphrodisiac foods to your diet. For centuries in many cultures certain foods have been renowned for their libido-lifting properties. Shellfish and herbs such as ginseng and yohimbe can give you a sexual boost. But there's also growing evidence that everyday foods -fruits such as watermelon, and vegetables - are also good for your libido. (Consult your doctor before adding any unusual herb to your diet.)

Adjusting your diet serves another benefit as well - it can help you to lose weight. Two of the most common reasons people cite for avoiding sex include feeling fat or unattractive, and having little energy. When you lose weight you feel more confident about your body and rev up your energy level.

Reconsider medications. Some drugs-such as some antidepressants or hypertension medications - can zap your sexual desire. Find out from your doctor if this is a side effect of any of drugs you're taking, and ask if there are alternatives that won't affect your sex drive.

Seek medical advice and counseling. About 43 percent of women and 31 percent of men suffer from sexual dysfunction. It can be caused by a variety of factors, including an underlying medical condition such as diabetes, or high blood pressure. In some cases, a religious belief or prior negative sexual event is the reason.

You can't resolve sexual dysfunction on your own. Visit your family doctor for a checkup first to address any health concern. If the problem isn't physical, he can refer you to a counselor or psychologist who can help to get you and your partner in sync sooner rather than later.