what makes you feel very weak

tried weak no energy

Simple fatigue is usually a result of lifestyle factors that stress the body, such as a lack of sufficient sleep, lack of proper nutrition, strenuous physical activity, a bit depression, or bereavement. Viral illnesses such as flu can leave you tired for weeks afterward. Sometimes, persistent fatigue is due to an underlying condition such as anemia or a thyroid problem.

For more details see below link:
http://homeremediesforyou.com/Fatigue