8 Surprise Reasons You're Still Tired

You've Gone Vegan...

Vitamin B12 is necessary for the growth of red blood cells. This energy booster comes mainly from animal products, but if you've given up meat and fish as well as eggs and dairy, you're at high risk for deficiency, Fryhofer says. In addition to feeling run-down and weak, you may also notice that you have pale skin that bruises easily, a sore tongue, bleeding gums and an upset stomach. A blood test can tell you for sure if your B12 levels are low. In the meantime, look for supplements with 100 percent of the recommended daily value of B12 and try to eat fortified cereals as well as nutritional yeast.