Maven, college can be very difficult for someone with a mental illness. Have you tried CBT for your OCD? Meds alone don't help everyone; sometimes therapy is needed. If you could break the power OCD has over your behavior, you wouldn't need to explain yourself. My brother has OCD (much milder than yours; he only has obsessions, no compulsions), and with medication and a year worth of therapy he is functioning extremely well. I had OCD symptoms when I was younger (like you, I was afraid of "contamination"; I washed my hands 30+ times per day till they bled). Logically challenging my obsessions really helped me (i.e. "most people don't get deathly ill or cause others to get deathly ill by not washing their hands after touching their hair. Chances are, if I touch my hair, I don't need to wash my hands.") I understand that simply reasoning through the obsessions may not work very well for you since your OCD is so severe, but it is something to try.

As far as telling professors about your MI, I suggest not doing it unless it is necessary and you are sure the prof will understand. I made the mistake of telling my experimental psych prof about my bipolar and ADHD, and he used it as an excuse to bully me. He made me cry twice. He gave me a "C" in the class even though I got "As" on all of the exams; he graded my final project extremely harshly.

Good luck with this situation!