Gut upset: quick tests.
A few very fast allergy tests.
In addition to the two-week exclusion diets there are some other markers for food allergies.
Test # 1:
Which are the food(s) you just can't do without? That's the foods you'll have to stop eating. It'll be tough for 2-3 days, and difficult for about 2 weeks, but then you'll feel so much better that you'll wonder why you ever did eat such poison.
Test # 2:
Take your pulse before and after eating something you suspect might be a problem. If it's 10-15 points higher within 15 minutes, stop eating that particular food.
Test # 3:
Food that has you running to the loo with explosive diarrhea pretty much immediately you've eaten it is a food you're severely allergic to. And such a food is extremely irritating to your gut.