(Health.com) -- Most of us already know that eating less and moving more are the keys to dropping extra pounds. But if you're already doing everything "right" and can't seem to lose weight -- or are even gaining it -- you may have a hidden health condition that's sabotaging your efforts. And the symptoms may be so subtle that even your doctor can miss them. Here, some possible weight-loss blockers -- and how to get the help you need.

A Sluggish Thyroid

Your thyroid gland makes hormones that regulate the way your body uses energy. An underactive thyroid (hypothyroidism) disrupts your metabolism, as well as many other aspects of your health. Some estimate that as many as 10 percent of adults have hypothyroidism, which is more common in women and is most often diagnosed in the 40s and 50s.

Could this be you? Besides weight gain or an inability to lose weight, you may notice fatigue, hair loss, dry skin, joint pain and muscle weakness, heavy periods, increased sensitivity to cold, even depression. Many people with low-grade hypothyroidism just feel "off," with no obvious signs of being truly sick.

How to get tested: Ask your internist to run a TSH (thyroid-stimulating hormone) screening. In general, the higher your TSH level, the slower your thyroid is. "While traditional 'normal' values are between .45 and 4.5, if your level is above 2, you might still struggle to lose weight," explains Dr. Jamie Kane, M.D., medical director of Park Avenue Medical Weight and Wellness in New York City. Your doctor may also want to check your levels of T-3 and T-4, the two main thyroid hormones. But hypothyroidism isn't always a straight numbers game; more and more doctors are now treating the symptoms, not just the blood-test results. "If a patient isn't feeling well, it's often because her thyroid isn't functioning as well as it should for her body," says Dr. Erika Schwartz, M.D., an internist in New York City.

How it's treated: Your doc will usually start by prescribing a low-dose T-4 thyroid hormone like Synthroid. If your symptoms don't improve, discuss upping your dosage or switching to a combination of T-3 and T-4.

Health.com: 25 diet-busting foods you should never eat

Out-of-Whack Hormones

As many as 1 in 10 women of childbearing age have polycystic ovary syndrome (PCOS), a condition in which a woman's ovaries produce an excess of male hormones. In addition to causing ovulation problems and infertility, PCOS may go hand-in-hand with insulin resistance, a glitch in the way your body processes blood sugar, which is often associated with excess fat storage, especially around the waist. Left untreated, insulin resistance can lead to type 2 diabetes.

Could this be you? You may have irregular periods, excess facial and body hair, acne, some male pattern balding, and trouble getting pregnant, along with unexplained weight gain (though not everyone with PCOS has weight issues).

Health.com: How carbs can help you lose weight

How to get tested: Your gynecologist or internist can test your levels of sex hormones for an imbalance of testosterone, progesterone, and estrogen, says Dr. David Katz, M.D., director of the Yale Prevention Research Center. She may then test your blood sugar and insulin levels or perform an ultrasound to check for cysts on your ovaries.

How it's treated: Lifestyle changes are usually the first step. If you're already eating a healthy diet and exercising regularly, you may have to kick it up another notch to see results. If you have insulin resistance, Katz says, you'll also want to cut out refined carbs and added sugars. If you've made these changes and still don't notice a difference, your doc may prescribe a drug called metformin, which is used to treat insulin resistance as well as assist with ovulation (if you're trying to get pregnant).

Health.com: America's healthiest superfoods for women

Trouble-Making Foods

Most people know if they're allergic to certain foods like nuts or shellfish, but many aren't aware of food intolerances. While a true food allergy results when your immune system mistakenly identifies a food as harmful and mounts an immediate response, food intolerances can have a variety of causes, including lack of a certain digestive enzyme (as with lactose intolerance) or sensitivity to food additives, and tend to manifest over time, says Dr. Elizabeth W. Boham, M.D., R.D., a family practitioner at The UltraWellness Center in Lenox, Massachusetts. Eating a "trouble food" -- the most common being dairy, gluten, eggs, soy, corn and nuts -- can lead to bloating and water-weight gain, among other symptoms. Experts estimate that food intolerances affect as many as 1 in 10 people.

Could this be you? You may regularly have bloating, gas, diarrhea, and constipation -- as well as seemingly unrelated symptoms like mild asthma, eczema, headaches, muscle and joint pain, and fatigue.

Health.com: The 50 fattiest foods in the states

How to get tested: An internist or gastroenterologist can help you diagnose the problem, but you can begin to figure it out for yourself through an elimination diet. Boham suggests that you start by removing gluten and dairy (these are the biggest culprits) from your diet for two to three weeks. If you don't notice a difference, also eliminate eggs, corn, soy, and nuts, and consider nixing additives such as food coloring and preservatives. After a few weeks, slowly reintroduce the possible culprits, one at a time, noting any reactions.

How it's treated: If the reaction is severe, you'll need to cut the offending food from your diet. For mild reactions, try a daily probiotic supplement, which restores the good bacteria in your gut necessary for digestion and can help prevent bloating and water weight gain. Boham recommends one with at least 10 billion live bacteria per pill.

Pills That Pack on Pounds

Weight gain can be an unwelcome side effect of some drugs, including antidepressants, steroids, and, more rarely, birth-control pills (due to a temporary increase in water retention).

Health.com: What to do when the drugs you need also put on the pounds

Could this be you? You may notice weight gain within a few weeks of starting a new medication, though it could take several months before you see any effects, Kane says.

How to get tested: No special test is needed; you know if you're gaining weight.

How it's treated: Talk to your doctor, who may be able to prescribe an alternative. In the case of anti-depressants, bupropion has been shown to cause less weight gain and possibly even lead to weight loss. With birth control pills, switching to a version with a lower dose of hormones might minimize weight gain. But remember, treating the condition you're taking the drug for is your biggest priority, so you should never go off any meds on your own.

Copyright Health Magazine 2011