The above link is a good place to start. What you put into your body, at what time of the day, has as much to do with how you feel as what it is made out of. I probably could have clicked on your profile, to find out your age and sex, which would have helped, but I didn't think of it.
Some things that can immediately affect the way you are feeling are:
-eat a peice of "breakfast" fruit in the morning. These include half a grapefruit, orange, kiwi or strawberry. Drink a full glass of water with the fruit, and THEN move onto the more heavy grain based cereal. It is generally reccomended that you have two servings of grain in the morning. This is a slice of toast and a 100cal or less bowl of cereal, two peices of toast, or something equivilent.
-SNACK AWAY. Seriously. You should be having a snack between breakfast and lunch, between lunch and supper, and one snack before bed. These should consist of a fruit and a glass of water. Not drinking enough water makes you very sluggish, and the natural sugars in fruit are an excellent way to nearly instantly improve energy, wakefullness, and mood.
-Lunch should be two(female) to three(male) servings of grains. Remember, potatoe and corn, nutritionally are grains.Whole grains are your best bet. You should also be eating about a cup of veggies, and a protein.
-Supper sounds pretty good really. Just be sure you are getting a proportionate amount of veggies.
*Always check what a serving size should be on a valid nutritional guide.Cut back on salt, it will do WONDERS. Try to drink water with every meal, and make sure to eat your fruits!
Ajust this of course, to suit your needs, but these are tips that will really help in the long run. If you start eating this way, which is rather flexable really, at first you will feel STUFFED and be shocked you are eating this much food, however, you may become very hungry when it is snacktime :P I would seriously reccomend doing some of these things, beacuse they DO help. Eating too little of certain things at meals, can be as harmful to your body as eating too much, and produce the same sluggish, tired, unhealthy feelings.
I am NOT an expert, but once I began following exactly what my body nutritionally shoudl have, and made it work for me as an individual, I feel so much more healthy.
-Seeing a doctor about how you are feeling is NEVER a bad idea-