Please Help!!!

For the past 5 years I have suffered from a constant clear, salty, sticky phelm forming in my throat requiring me to 'hack' it up and spit it out. At least a few times everyday I find myself having to do this, but whenever I have a cold or flu the condition goes haywire and out of control forcing me to hack up about half a litre of phelm per day. Sleeping is also a problem as the phlem seems to increase whwn I lay down. The problem first started about 5 years ago when I used to smoke cigarettes. I quit smoking because of the problem and I have not had even a whisp of smoke in my lungs for 5 years, but still the problem persists. I have had my lungs checked and they are clear. I have been told a specialist that it may be a reflux problem but why then is it effected so much when I get a cold. Please help me as it is the bane of my existence and has destroyed my quaility of life.