If you are sleepy through most of the day then you are either not getting enough sleep or not getting enough nutrition. Lack of sleep in the night or disturbed sleep will eave you feeling drowsy through the day and you will have lower productivity. If nutrition is causing the lower levels of energy then you can definitely sort that out during the day. The key is to understand what the contributing factor to your situation is.
If you are sleepy as a cause of lack of sleep then you must avoid eating heavy meals during the day it will only cause havoc in your system. Avoid dairy products like milk and cheese as they are heavy to digest and will lead you toward sleep. You can have a fruit salad or a fruit punch for breakfast, followed by salad or a sandwich for lunch. Keep snacks minimal and opt for protein rich snacks like dry fruits that are nutritious. You may choose to have a heavy dinner so that you are able to sleep well at night.
Eating something extremely sour or spicy will wake you up instantly. You must have an energy drink or an energy bar during the day to up your energy levels so that you may maintain productivity. Sports drinks are a healthy option. Avoid coffee and caffeine drinks as they are not healthy and provide only short term relief.
If nutrition is causing you to be in the dilemma that you are in then you must do the exact opposite of what you would do in the case of lack of sleep. Have a healthy breakfast with either Porridge or breakfast cereals with a glass of milk. Have a fruit to end the breakfast. Choose to have a bagel or waffle as a snack and a fruit juice later in the day. Include carbohydrates in your meals during the day and stay clear of junk food as they load you up with unhealthy fats. Dairy products like yogurt and buttermilk will help you in your condition.