A 26-year-old woman presents to the GP with cyclical mastalgia (bilateral breast pain) that peaks in the luteal phase and resolves after menstruation. She has no lumps and her examination is normal. She rates the pain at 7/10 and it affects her sleep. First-line measures (well-fitting bra, paracetamol, NSAIDs) have not provided sufficient relief. Which is the next most appropriate step?