it sounds like you're eating way too much sugar and carbs, and not enough protein.
protein will give you long-lasting energy & satiety. what i do is pair a carb with a protein for my meals. for lunch today, i had cheese & crackers and blueberries. also, i eat about 300 calories every 3-4 hours, which has given me a ton more energy than eating fewer, larger meals. do you exercise? while you're at work, try snacking on protein, like nuts. i always take a little bag of almonds with me to work, or cheese & crackers.