I have the same problem you have--when I eat certain foods, I have symptoms of mucous build-up such as snotty nose, excess phlegm, etc.
Here's the solution.
1) Keep a food journal. Write down everything you eat and drink.
2) Whenever you get the mucous build-up, check what you ate within the last 12 hours.
3) Eliminate those foods.
4) Milk causes mucous. So do white-flour products like cheap breads and pastas, donuts, cakes. Milk is really harmful. Visit: http://www.milksucks.com and http://www.notmilk.com and http://www.nomilk.com
5) Fast. Go for two-to-three days without eating anything.
6) Only drink water with a teaspoon of honey and some fresh lemon or lime juice squeezed into it.
7) When you begin eating again, start with a big glass of water for breakfast, with a teaspoon of honey and a tablespoon of Bragg's organic apple cider vinegar. For a snack, an hour later, eat fresh fruit. For lunch, have a spinach salad with olive oil and lemon for dressing, with other veggies. You can add tuna if you like, or a boiled egg. For dinner, have a baked sweet potato, brown rice, butter (margarine is a poison) and some lightly steamed veggies.
8) And drink lots of water inbetween.
9) Eliminate sodas, milk, pasta and breads and cakes--stuff containing white flour.