Tired, sluggish and can't seem to lose weight? Or are you running around like crazy with a heart rate that's speeding out of control? Your thyroid may be to blame. This tiny gland, located at the front of your neck, makes and secretes hormones that play a part in nearly every system in your body, from your muscles and bones to your brain, heart, liver, gut, skin and reproductive organs. And if it's not functioning at its best, it has the potential...