I've used a waterpik with the nose attachment and a simple saline (salt water) solution. Really clears things up in there. Once you get used to the feeling....
Diet helps too. I never believed it, but I used to eat crap food all the time. I cleaned my diet up, more leafy greens, veggies, and whole foods. Dropped 20 lbs and my allergies all but went away. Occasionally get a stuffy nose during the peak pollen, but that's it.