What do I have?

EDIT: Right as I hit "Submit" I realised the title might be interpreted as a call for a diagnosis. It is not. My apologies.

TL;DR: I feel like I've lost what defines me, the thing that made my life worth living, and I don't know how to proceed.

Long version: I've always fancied myself a somewhat intelligent person, which is really the part of me I've always clung to. Surely, I once heard someone say that the value of a person to society and the people that inhabit it is made up of three parts: Intelligence, personality and looks. And as I've always lacked any positive shade of the latter two, I have had to contend with the former. I built up a person, a personality, a mindset around my belief in my intelligence.

Come last Friday: I was given a B in religious studies, though my teacher told me that were I more active in class, she would give me an A instead. I then proceeded to raise my hand every chance I got, finding myself brutally shot down every single time. Despite my good grades (mostly B's and A's, I'm the equivalent of a junior in HS) I have always questioned that "intelligence" I thought, and everyone else assured me, I had. Now I had my confirmation.

God, I wanted to curl up in a corner and cry so badly. I can't remember feeling worse than that, emotionally, inside. As I questioned the one thing I could always cling to, the thing that had always defined me, I felt like the very foundation of my existence started to crumble.

Did you ever watch that episode of Friends, during which, in a flashback, Monica offered someone else her last Kit Kat bar? That, in my mind at least, is what defined that Monica, in some obscure and, I suppose, rather derogative way. But that is who I longed to be. I longed for something to define me, something I could care about. Not necessarily something to make me happy, but something to make my life not seem like a waste, like I'm worthless.

Some time ago, I saw a picture of a child lying amid a sea of Pokémon toys. That's how I want to be. But I don't know how. Do I just get over myself? Find something else to cling to?