Nose / Sinus :: Constant Mucus In Throat

Ok so I've had this problem for over 2 years, and its the biggest pain ever. I ALWAYS, and I mean ALWAYS feel Mucus in the back of my throat, I can't clear it away by just coughing it up, or spitting it out, I have to suck it in me. I really try to spit it out, but I can only spit it if I let it build up for awhile, other than that I have to suck it up, and while doing that I make a really annoying noise....something like blowing your nose really really hard, but even worse noise. I talked to my parents but they never believe me, they tell me: Its Psychological, and I've adapted a bad habit.But I SWEAR I can feel it always. We've been to a Allergist, and he said its maybe Sinus, or Post-nasal drip. He said the Mucus builds up in my nose, and drips down to the back of my throat...Although I can't feel the drainage from Nose to throat, but my nose is pretty blocked up. The Allergist said this started because of a past allergy, and I agreed. 2 years ago I had severe Allergy, and once the allergy left, this problem continued on till today.The Allergist recommended Nose drips, and Allergy medicines, but they never helped not even a bit. Next we went to a Nose and Throat Specialist, and she checked my nose and throat and said: Its Psychological, and I've adapted a dirty habit. But I SWEAR on my life, I feel it 24/7 in the back of my throat, but no one believes me not even the DOCTORS! What shall I do PLEASE help. This Mucus is always there, and by clearing my throat (Spitting, Sucking whatever), its makes a noise, that every hates, even MYSELF!!!  PS. I tried drinking salt water and everything.