A 29-year-old single woman presents to the PMHNP for evaluation of a chief complaint of fatigue. She states she has been feeling "tired" and "empty" for the past 4 years. She sleeps up to 11 hours a day and is still tired. She has trouble concentrating and has difficulty making decisions. She has gained 10 pounds over the past 2 years due to overeating and little physical activity. She reports no suicidal ideation or manic symptoms, and no delusions or hallucinations. What is the most likely diagnosis?