Will, I recently saw a report, published as a letter to a medical journal from a doctor, that attributed a similar condition to aspartame use.  This wasn't even close to research, but he had (IIRC) 4 patients in which withdrawal of aspartame stopped the condition, and in most if not all of the cases, it came back immediately when the patient ingested aspartame again.  In a teenager the most likely sources of aspartame are diet sodas and sugarfree gum, though it's likely in any product that claims "reduced sugar" or even "no sugar added."  The effects should be fairly immediate, and it can't hurt to try.