A female complains of significant weight loss without dieting. She also complains of anxiety, heat intolerance, insomnia, shakiness, and an increased number of bowel movements without diarrhea. She has no past medical history, takes no medication, and does not drink or smoke. Family medical history is significant for diabetes and thyroid problems. The exam shows tachycardia, resting tremor, mild exophthalmos, conjunctival injection, and lid lag. The thyroid is 3+/4 enlarged without nodules and is non-tender. What is the most likely diagnosis?