Suggest Treatment For Chronic Blocked Nostrils And Post Nasal Drip

I have had post nasal drip for years and it worse since I had septoplasty and balloon sinuplasty. Have tried many nasal sprays, sterimar, neti pot, antihistamines, rinatec, reflux medication, sinus wars, montelukast I drink lots of water too but nothing helps. I clear my throat and have a stuffy nose 24 x 7 all year so there is no respite. On montelukast currently but mucus is thicker so will not continue. Allergy expert tested me and it only came up with grass pollen. Do you have any suggestions please?