There are two types of bipolar disorder, Bipolar 1 and Bipolar 2.
Bipolar 1 is the version with the obvious swings.
This drug Lamictal seems to be working on Bipolar 2, I know a lot of people who get more depression symptoms and cannot remember a manic moment (but if they do, it was only once in their life.) I do know that my good friend with BP2 has MAJOR problems when she isn't on the right medication, but mainly only during PMS time. Lamictal has literally changed her life, all for the better, and it's not like she was low functioning to begin with., it just made facing everything she was dreading daily, the overwhelming stuff, a LOT easier to see the light at the end of the tunnel.
I personally would not medicate a young teen. A lot of kids have a lot of issues dealing with their hormones, as do we all, and many antidepressants have the unpleasant side effect of causing suicidal tendencies (especially in teens.) I don't know that Lamictal is one of these, but it's worth trying other approaches (granted, I don't know what else you have done, so maybe a pediatric psychiatrist has already talked to you about it, but I would go to Dr. Amen's clinic in Fairfield for some blood flow studies and education about children's mental health to see if it's anything organic first even if I've spoken to other specialists.) good luck!!!!