Heavy Period!

I usually get light to medium periods on time every month for four days but this month I was two days late and am EXTREAMLY heavy (I'm only 2 days in to my period) and it's to the point where I am over heating, not hungry, light headed, nauseus and dizzy. I can't go to my doctor because you have to book an appointment 2 weeks in advance. I am dreading going to school tomorrow because I am going through a lot more tampons that usual and keep bleeding through. I bleed through the tampon at night and I am using the super size ones. Before anyone says I am just developing, I know that I am not because I started my period 2 months after I turned 10 and I am almost 16 now and am fully developed in my body. I honestly don't know what to do. And I can't skip school because I have exams. Any advice?