3 YEARS - stuffy nose, post nasal drip, ruining my life!?

I've had this forever. It all seems to be related, sometimes its better than others but for the majority of the time it really effects how I talk, breathe, etc... I'm constantly clearing my throat, I can hardly breathe through my nose and it gets clogged and switches sides, and on really bad days my throat get so congested and soar from the clearing that I can't even speak. I'm 14 years old, this started sometime around 3 years ago. I'm not sure exactly when...Doctors prove useless, I've been to countless doctors numerous times, I've been to several specialists...I've had 88 needles pricked into my back, I've had a camera in my nose looking for polyps, I've had blood taken... I've had thorough allergy testing which all appeared negative besides one. They said I "might" be allergic to pollen and dust mites, so now they have me back on nasal spray which does absolutely nothing. This is driving me crazy and its going to cause me to fail my cles because it's so distracting when I'm trying to learn and pay attention. Please, someone help me, I beg of you. I've been contemplating suicide for a while, because this is driving me to the brink of insanity.