Final answer:
The most appropriate next step in the management of this patient's symptoms is to obtain a symptom diary for two months.
Step-by-step explanation:
The most appropriate next step in this patient's management is to obtain a symptom diary for two months (option A). This will help track her symptoms and identify any patterns or triggers. By keeping a record of her mood swings and fatigue in relation to her menstrual cycle, the patient and her healthcare provider can gain insight into her condition and develop an appropriate management plan. Other options such as recommending dietary changes (option B), beginning treatment with an anxiolytic agent (option C), referring for psychiatric consultation (option D), or obtaining a pelvic ultrasound (option E) may be considered in the future depending on the findings from the symptom diary.