Sir i feel very weak sometimes.my body is not so strong.what foods should i eat to increase my body energy?

Go see your doctor: If you feel very weak, best to go see your doctor for a complete evaluation to make sure it's not due to anemia, hypothyroidism, depression, etc. Once cleared, then focus on eating healthy, eg lots of fruits & veggies, healthy fats & oils, lean protein, etc. Your doc can also refer you to a nutritionist for more specific answers. But while waiting, check out mediterranean diet.