I don't think that protein is needed for long term energy. Protein *can* be energy, but it takes a while to turn it to something usable.
Instead, what might help you best it to eat foods that are high in low glycemic carbs... or carbs that "burn slow". My suggestion: lots of old fashioned, no-sugar added, non-precessed, creamy oatmeal. Or do what i do: eat the oatmeal (with a large helping of Maple Syrup), and then take a snack to school. EVERYONE, meat eating or not, tends to need a snack 2.5 hours after breakfast.
The reason you might've not needed a snack before (which I always needed as a meat-eating teen) might have to do with total calorie intake.
The difference might be that you used to eat a lot more CALORIES at breakfast. Vegan foods can be filling, but low in calories. Thus, your stomach is often full, but you've had a lot less calories consumed. There are two solutions. Snack (yummy), or eat a lot more (yumm). Either way, you win.
"The worker has the right to leave his boss, but can she do it? And if she does quit him, is it in order to lead a free life; where she will have no master but herself? No, she leaves to sell herself to another employer. She's driven by the same hunger. Thus the worker's liberty is only a theoretical freedom, lacking any means of realization; an utter falsehood."