Dear Minh Anh,
I was sorry to hear about your problem. Here's what I think you should do to prevent allergy. I strongly recommend that you should stay away from the food that make you allergic. The most commonly causing allergies are: shellfish, milk, eggs, peanuts anh so on. Allergy isn't usually serious so if you are allergic you will need paramedics on the scene as soon as possible. If you have allergies and it makes you have trouble breathing ,has swelling of the face or lips, or develops severe vomiting or diarrhea after eating, call 911 or your local emergency number right away. You should keep away from acohol and do not smoke when having allergies.
I hope that my advice will improve your situation.