How Can A Swollen Lip Vesicle Be Treated?

I have a huge swollen blister in the middle of my upper lip. I can't even close my mouth or talk properly it's so big. My mum days it's because I've been coughing and then ate a jar of peaches, or because I haven't been brushing my teeth. It doesn't hurt, even when I touch it though. How long will it be there because I have a trip on Monday. I already skipped two exams so I could stay home and rest!