Two Years Ago I Suddenly Became Unable To Tolerate Cooked

Two years ago I suddenly became unable to tolerate cooked or melted cheese, even in small quantities, for the first time in my life. No effects at time of eating, but violent cramps and one or two extreme episodes of diarrhea occurring 6-8 hours after eating cooked cheese. Happens every time, and whatever I combine the cooked cheese with. I use a hard, high-fat cheese (Cornish cheddar) for cooking, and can eat unlimited quantities of the same cheese if it's uncooked! No problem with other dairy products, including cheeses, and I've never been lactose-intolerant. Could be age-related - I'm a 71-year-old female and have noticed there are some other things I can't digest as I get older (e.g. apples, mushrooms, stone fruits). Don't know whether it's a coincidence, but started after a three-week course of high-dose broad-spectrum antibiotics following a throat injury two years ago.