why do toothaches have to hurt so bad?

I broke my temporary cap again over the weekend. Teresa got me some stuff that's supposed to re-cement it, and it's kinda working but I must really clench my teeth in my sleep lately, because it's nothing but a bruise right now. I have no idea how I'm going to make it through the day. I have a meeting at 1:00 that I'm in charge of, and a group meeting before class today for a different class's project. Would a mouth guard help in this situation, or would that put pressure on all my teeth?