I try to not eat the things that make me feel unwell, but I do eat them on occasion. Sometimes because I am weak-willed--a little taste of birthday cake, or a little flan at the Mexican restaurant. I always pay, however, and wonder why I caved. But sometimes gluten and dairy lurks in food and I eat it unexpectedly. It's not until I get symptoms do I realize this has happened.
Wheat is in many foods, and so is dairy. If you read labels you will be more apt to not get ingredients that make you sick. Look at the ingredient list--how dairy or wheat can be listed.
If you ask at restaurants, being specific that you are eating dairy free and wheat free, you can usually get your meal customized. Don't feel bad about this...it's your health you're protecting. I've talked to many people who think they are complaining and feel badly about it. Students who attend culinary school are being taught how to tend to people with allergies or intolerances. So be assertive and you'll be rewarded.