First a couple disclaimers:
#1 I am not a dietician. #2 the fact that I am dispensing diet advice is a bit of a hoot. And while I am far from a fast food junkie I will confess to a HUGE weakness for a certain potato product from a certain golden-arched establishment.
But there really ARE some simple things you can do, diet-wise, to help with your sinus problems. The degree to which you try this stuff can be adjusted based upon how bad your sinuses are.
The first is to eliminate dairy. Eggs might be ok, but try and look at lactose-free milk, cheese, yogurt, etc. Soy substitutes can work really well too.
Second, try and eliminate wheat. And yes, I realize that this one is even harder than the first. Health food stores or Whole Foods should have substitutes.
Dairy and wheat are the two main culprits. And unfortunately they are also two of the more common things found in the food we love. It should also be said that you don't have to go completely wheat/dairy -free, nor do you have to do both at once. Experiment with simply easing back a bit and take it from there!
It can be done, and I have seen folks close to me have great success once they commit to sticking to it!