Bad Breath (Since 4. 5+ Years) Advance!

Hello doctor, I am 21 yrs old male from Nepal. I am suffering from BAD BREATH and SORE THROAT since more than 4.5 years. I thought it was due to frequent common cold and will pass away but it didn't. Now my condition has worsened. I consulted two doctors here in Nepal, but none of them took this problem seriously and couldn't give me satisfactory causes and cure for it. One of the doctors told me I am having DNS. When I cough or sneeze greyish black (now a bit clearer than before when I started doing nasal rinse with salt water with soda) comes out. Most of the times I have a feeling that something is there in my throat. I am being embarrassed due to this bad breath but the doctors here are not taking me seriously. THANKS IN ADVANCE