Problem Foods for upset stomach

My last post was not saved so this will be a shortened version of it. I find that I have problems with certain foods. I thought I may be lactose intolerant. I experience upset stomach after eating a bowl of cereal, but I eat pizza everyday (i work at a pizza place) with no problems.

I've had trouble with certain foods that contain mayo as well. Potato and macaroni salad tend to upset my stomach. But tuna and chicken salad do not. Nor does any other sandwich with mayo.

I try to stay away from problem foods, but others are turning up. Like a pork burrito at a mexican restaurant down the street. I've eaten that same burrito everytime I've gone for the past year with no problems up until the past 2 times. Chinese and Japanese food have never bothered me up until about a year ago. Now I can't get home fast enough.

I can drink a iced latte and have problems. But the same ingredients, with the same amount of milk, in a hot latte gives me no problems. Would steaming the milk make a difference?

After eating those problem foods, I'll have an upset stomach but once I can "relieve the pressure", I'm fine so I don't think it's a food allergy. No hives or irritation or anything else. Can anyone see a pattern or even a certain ingredient that would be the trigger to an upset stomach? Thanks for your time and help.