Attention Deficit Hyperactivity Disorder (ADHD): Charles's symptoms of difficulties with focus, concentration, and organization since childhood, along with his struggles to sit still, excessive talking, and difficulty relaxing, are classic symptoms of ADHD. The fact that his symptoms have intensified with the increased academic workload and that he has never been diagnosed or treated for a mental health disorder supports this diagnosis.

Anxiety Disorder: Although Charles denies a history of anxiety, his difficulty falling asleep, waking up multiple times, and feeling restless could be indicative of an underlying anxiety disorder. The pressure of his academic workload and his struggles with concentration could be exacerbating these symptoms.
Depressive Disorder: Charles's reports of mood and energy fluctuations, feeling moody or depressed, especially when behind in his schoolwork, could suggest a depressive disorder. However, he denies a history of depression, which makes this diagnosis less likely but still possible given the context of his current struggles.
Sleep Disorder: Charles's difficulty falling asleep and waking up multiple times could indicate a sleep disorder, such as insomnia, which might be contributing to his concentration and focus issues.

Bipolar Disorder: Although Charles denies any history of mania and there's no family history of bipolar disorder, his mood and energy fluctuations could potentially be indicative of a bipolar spectrum disorder. It's crucial to carefully assess for any manic or hypomanic episodes, especially given the potential for mood stabilizers to exacerbate untreated bipolar disorder.
Substance-Induced Disorder: Despite Charles's report of no substance abuse beyond occasional alcohol consumption, it's essential to consider the possibility of substance use contributing to his symptoms, especially given the potential for substances to affect concentration, mood, and sleep.

Neurodevelopmental Disorders (e.g., Autism Spectrum Disorder): While less likely, some of Charles's symptoms, such as difficulties with social interactions (talking excessively, finishing others' sentences), could potentially be part of a neurodevelopmental disorder spectrum. However, this would typically be associated with more pronounced social and communication difficulties from an early age.
Medical Conditions with Psychiatric Symptoms: Certain medical conditions (e.g., thyroid disorders, sleep apnea) can present with symptoms similar to those Charles is experiencing. Although he reports no history of cardiac issues, seizures, or glaucoma, a comprehensive medical evaluation might be warranted to rule out any underlying medical conditions contributing to his symptoms.