Muse, I had the same problem with the guidance counselor at my high school, because my official name is "Margaret" he decided my nickname was "Peggy" (go figure!) so he'd call me Peggy, which is not even close to my nickname. I'd have to "translate" when I'd see him looking at me as we passed in the hall or something and he'd say "hello" to "Peggy" and be sure to answer back.

How about other relatives besides your parents? Do you have an older sibling you can confide in who can break the news to your parents or an aunt/uncle, etc.?

I'd think up a "plan" do a little research on how you can find out the other info you would like to know (how about your family doctor/pediatrician, can you ask your Mom to take you to/see him? He can break it to her in a way she'd have to buy it?) and then work through your plan (pretend you're doing a project for school, the result being to get interviews with 2-3 different therapists, how would you organize it?).

You might read this stuff http://www.metanoia.org/ it's very good, solid info.

You could get in a conversation with your Mom about when she was a teenager, the problems she remembers having and how she solved/approached them and then break it to her that way, that you'd like to see someone professional to discuss some of yours?