A 28-year-old woman reports a 1-year history of intermittent crampy lower abdominal pain relieved by defaecation, with bloating and alternating constipation and diarrhoea. She has no rectal bleeding, weight loss, nocturnal symptoms or family history of bowel cancer. Examination and blood tests including full blood count, coeliac serology and inflammatory markers are normal. What is the most appropriate management?