What Causes Persistent Stuffy Nose Along With Mucus In Throat?

For 7 + years I have been dealing with mucas in my throat. Alot of mucas. My nose is always stuffy. I have had sinus surgery. No improvement. I recently had a scope placed down my throat, my dr said everything is normal. I noticed when the weather gets warmer, breathing it next to impossible. I have been to an alergist. I have no alergies. This all started when I had bronchitis. It cleared up , but my problem started. My life is suffering. Working is almost impossible. Thank God my job understands. I dont know where else to go. I have already spent thousands with no answers. Please help.