A 28-year-old woman presents to an outpatient gastroenterology clinic with a 3-month history of chronic gastrointestinal symptoms. She recently returned from a tropical vacation where she experienced a severe diarrheal illness, which resolved with supportive care after approximately 72 hours. Weeks following her recovery, she began to experience recurrent episodes of bloating, significant flatulence, and watery, non-bloody stools. These symptoms consistently occur within one to two hours of consuming dairy products, such as her morning latte or creamy soups. She denies any fever, unintentional weight loss, or blood in her stools. On physical examination, her vital signs are stable. Her abdomen is soft, non-distended, with mild generalized tenderness on deep palpation, and active bowel sounds with audible gurgling (borborygmi) are noted. There is no hepatosplenomegaly or palpable masses. Rectal examination reveals normal tone and no gross blood. Stool occult blood test is negative. Her complete blood count, serum chemistries, thyroid-stimulating hormone, and erythrocyte sedimentation rate are all within normal limits. Stool pH is 5.5 and stool reducing substances are positive. C-reactive protein is 1.0 mg/L. Given her presentation, what is the most likely diagnosis, and what is the primary recommendation for her initial management?