I haven't had this problem that you've had, but trust me you are not the only one. The thing about us OCD people, is that we think we are the only ones in the world who are suffering from the problem, but we're not. There is so many of us out there that are suffering from the exact same problems, some more extense, some less extensive, and some with weird combos and some with normal combinations. However, it can be a part of it. You may be obsessed with being overweight and you do something compulssive like bulimia. Many people obsess about their weight and sometimes do drastic things to deal with it. It is an obsession and i would advise you to go see a counselor or a therapist. Accept it. And be willing to follow their orders and advise. Hey, you are not the only one. Take care of yourself, and know that you will be fine if you take that first step. Anyway, i hope you make some progress.
I've had both at once. When I was in college, I had bulimia and I have had OCD since I was nine, but just got diagnosed officially a few years ago. Right now I am on Prozac, Abilify, Vistiral, and Trazadone. I think both bulimia and OCD are supposed to be connected with serotonin. I would definitely consider seeing a psychiatrist with experience in treating both. I know it has helped me a great deal. Therapy and medication for me has helped.