My wife moved from Thailand to the USA 5.5 years ago.
The first three years, she had no problems with her diet, the first day on arrival we went out for pizza.
She has become very lactose intolerant, and your diet would automatically give her diarrhea all day long.
The whey protein would do it to her. We know because she has tried some of mine. Most types of cheese, but not all cheese. Any premium ice cream with high milk solids.
You can become lactose intolerant later in life. I would cut out all the sources of lactose like whey protein and see if it helps.
Outside of that, you can develop food allergies later in life. Since you have such a regular diet, change it and see what happens. Start with the obvious, sources of lactose.
Or go to a gastro specialist, they will likely do the same sort of thing.
