Coughing so much because of mucus in my throat (i'm tired of this) plz help any solutions or recommendations?

I've had excessive mucus in my throat for many years. It all started when I had a bad cold at the age of 12. I still have it. I had a cough that lasted for many months after I had gotten over the cold. After the coughing finally stopped, I've had the mucus in my throat ever since. I'm now 15 years old. That is a long time to suffer. I have to constantly clear my throat because I feel that I will be unable to speak or even breathe if I don't. It feels like there is a glob of mucus just hanging right where my vocal cords and wind pipe are. There are times when it isn't as bad and then there are times when I feel I will choke on it. It is worse in the mornings and after I eat anything. I don't even have to eat dairy products or drink milk for it to happen. That's why I don't think it is a lactose intolerance or allergy. I don't have heartburn or any other acid reflux symptom that I can think of. I know someone who has a similar problem and a doctor told her she had acid reflux. But the medicine he gave her didn't help. For me, the mucus in my throat is many times accompanied by an excessive amount of thick, clear mucus in my nose but not always. My mother has had the same problem for many years, also, constantly coughing up the mucus. My sister is just now beginning to have the same problem. Neither of us have ever smoked a day in our lives and neither of us live with a smoker. I've been to a doctor who gave me samples of every allergy medicine out there. None of them worked. As a matter of fact, the Allegra, Flonase and Rhinohort sprays that I tried gave me allergy symptoms that I never have, such as sneezing, runny nose and watery eyes, making me worse. I've recently tried Mucinex and so far am not impressed with it, either. It has really become a problem lately because people at work are complaining that my constant throat clearing is getting on their nerves. They think it's just a nervous habit and even had the supervisor approach me about it. One person even sent me a nasty e-mail, telling me to stop. She almost got fired for being so nasty to me. It hurt my feelings and made me angry because I can't help it. My mother went to an ear, nose and throat specialist and all he did was give her medicine that didn't work. We are beside ourselves on what to do. I wish we could find a doctor who would be willing to find out what is causing it instead of giving us medicine that doesn't work and send us out the door. If anyone out there can shead some light on this problem I would appreciate it so much!