Millions of Americans describe themselves as exhausted on a daily basis, many of them shuffling through life with little energy for enjoyment or satisfaction.

The first step in combating weariness is understanding why you're so tired. For some, the reasons may be obvious ... a newborn in the house, a stressful life change, a health issue or even the time change you forgot about. But for others, the reasons may be more clandestine. The primary causes of exhaustion are issues dealing with sleep, diet or exercise. Take a look at each of these and find out which one fits your situation and what you can do about it.

1. Sleep. Like I said, some of the reasons for fatigue may be obvious and a lack of sleep is definitely one of the more blatant culprits. But why are you having trouble sleeping? Some causes of sleep issues — like poor diet or lack of exercise — are controllable. Others, like the birth of a new baby are less so. For parents of newborns, rest assured that babies aren't babies forever and most little ones will start sleeping through the night within a few weeks. But if a new baby is not the cause of your sleep trouble, try avoiding alcohol and caffeine, turn off the TV and other screens within an hour or so of bedtime, and try going to bed and waking up around the same time each day to get on a better schedule.

2. Diet. Let me guess. You start the day with a caramel macchiato latte and a blueberry scone only to crash with fatigue before mid-morning. And you combat that sleepy feeling with another latte and maybe a bagel to hold you over until lunch. The caffeine-sugar-caffeine cycle brings on a wild ride of ups and downs. Sure, caffeine and sugary foods may give you a rush, but that rush rarely lasts long. Your better bet is to reach for water and a healthy snack when you are tired to give you a longer-lasting burst of sustained energy. Speaking from experience, if you decide to give up the caffeine and sugar cold turkey, be prepared for a whopping headache. Just pump the water and hang in there for a day and you'll be good to go.

3. Exercise. A healthy dose of exercise not only gives you more energy during the day, it also helps you sleep better at night. Even a 10-minute walk can give you more lasting energy throughout the day than a caffeinated calorie bomb from the coffee shop. But who wants to exercise when you are exhausted? Start slowly with an easy walk around the block after dinner, during your lunch break, or whenever you can squeeze it in. Every few days, add several more minutes to your walk or pump up the speed to improve your fitness and your energy level. With your doctor's approval, aim for about 40 minutes of exercise at least four days each week.

While sleep, diet and exercise can greatly affect your energy level, they aren't the only culprits. Chronic fatigue can be a symptom of other health issues such as anemia, thyroid problems, vitamin deficiencies, depression or heart disease. So if you are still exhausted even though you are exercising regularly, eating a healthy diet, and taking steps to improve the quality of your sleep, it might be time to check in with your doctor to find out if other health issues are the cause.