How do I get a medical condition exemption from my doctor so that I don't have to live in the dorms anymore?

I am currently a sopre in college and I don't want to live in the dorms anymore because I never stay in my room and they are just too expensive to have if Im not staying there. My school will only let you live off campus if you have a medical exemption, or you commute from home. I want to get an exemption because I think I am allergic to dust mites.