I am afraid that it is a little difficult to give you a diagnosis based on such scant facts. You have not mentioned how old you are, or how much you weight. If you are overweight then the best remedy for lethargy would be to begin a strict regime of physical exercise. In your case it is advisable to see the doctor who will be able to physically examine you and take note of other relevant symptoms.
You can try cutting down on food that is heavy and rich in sugar, cheese, white flour and oil. Eat a variety of fruits throughout the day. Avoid drinking carbonated drinks or too many cups of coffee or tea. Instead drink plain water. You can also drink warm water with lemon juice and some honey in it. Substitute sugar with honey, which is a healthier option. Avoid large meals. And completely cut down on eating in between meals. Take a brisk morning walk. Ensure that you get sufficient sleep. If you are worried about something you should try to get out of this since you often end up over- eating when you are tensed. You can practice some easy relaxation techniques to ensure that you don't feel stressed.
answered by G M